Permanent magnet synchronous motor

ABSTRACT

A synchronous motor includes a stator, a rotor and permanent magnets. The rotor includes a rotor iron core and rotatable relative to the stator, a plurality of conductor bars accommodated within corresponding slots in the rotor iron core. The conductor bars have their opposite ends shortcircuited by respective shortcircuit rings to form a starter cage conductor. The rotor also has a plurality of magnet retaining slots defined therein at a location on an inner side of the conductor bars, in which hole permanent magnets are embedded.

This application is a divisional application of U.S. patent applicationSer. No. 10/019,286, filed Jan. 2, 2002, now U.S. Pat. No. 6,727,627which was the National Stage of International Application No.PCT/JP00/04693, filed Jul. 13, 2000, the disclosures of which areexpressly incorporated herein by reference in their entireties. TheInternational was published under PCT Article 21(2) in English.

TECHNICAL FIELD

The present invention generally relates to a permanent magnetsynchronous motor and, more particularly, to the synchronous motorgenerally used in a motor-driven compressor in a refrigerating system oran air conditioning system or any other industrially utilized electricappliance.

BACKGROUND ART

A self-starting permanent magnet synchronous motor operates as aninductor motor at the time of starting thereof owing to a startersquirrel cage conductor and as a synchronous motor as rotating magneticpoles created by the permanent magnets are entrained by a rotatingmagnetic field formed by a stator winding and moving angularly at asynchronous speed upon arrival of the rotor at a speed approaching thesynchronous speed. This synchronous motor has an excellent constantspeed operating performance and an excellent high efficiency. Inparticular, various improvement have hitherto been made to a rotorstructure of the synchronous motor.

For example, the Japanese Patent Publications No. 59-23179 and No.63-20105 discloses the prior art rotor structure for the self-startingpermanent magnet synchronous motor.

FIG. 6 illustrates the prior art rotor disclosed in the Japanese PatentPublication No. 59-23179. Referring to FIG. 6, reference numeral 1represents a rotor, and reference numeral 2 represents a rotor iron corehaving a plurality of slots 3 defined therein adjacent an outerperiphery thereof. Conductor bars 4 are disposed within those slots 3and have their opposite ends shortcircuited by respective shortcircuitrings to thereby form a starter squirrel cage conductor. Theshortcircuit rings (not shown) are made of an annular electroconductivematerial disposed on axially opposite ends of the rotor iron core andare connected with the conductor bars 4. A plurality of magnet retainingholes 5 are provided on an inner side of the conductor bars 4, withcorresponding permanent magnets 6 embedded therein. Reference numeral 7represents magnetic flux shortcircuit preventive slits that are spacedsuch a small distance P from the magnet retaining holes 5 that magneticsaturation can take place between the magnet retaining holes 5 and theslits 7 to thereby prevent the magnetic fluxes emanating from thepermanent magnets from being shortcircuited between the differentmagnetic poles.

FIG. 58 illustrates a longitudinal sectional view of the rotor used inthe prior art self-starting synchronous motor disclosed in the JapanesePatent Publication No. 63-20105 and FIG. 59 illustrates across-sectional view taken along the line A-A′ in FIG. 58. Referring toFIGS. 58 and 59, reference numeral 11 represents a rotor, and referencenumeral 12 represents a rotor iron core made up of a laminate ofelectromagnetic steel plates. Reference numeral 13 represents conductorbars having their opposite ends connected with respective shortcircuitrings 14 to thereby form a starter squirrel cage conductor. Referencenumeral 15 represents permanent magnets embedded in the rotor iron coreto form four rotor magnetic poles. Reference numeral 16 representsmagnetic flux shortcircuit preventive slits each operable to prevent themagnetic fluxed between the neighboring permanent magnets of thedifferent polarities from being shortcircuited. Reference numeral 17represents an end plate disposed on each of axially opposite ends of therotor iron core 2 by means of bolts to avoid any possible separation ofthe permanent magnets 5 from the rotor iron core 2.

When the prior art permanent magnet motor of the type provided with thecage conductor is to be used since the conductor bars and the permanentmagnets are employed as rotatory drive elements, if the conductor barsand the permanent magnets are incorrectly positioned relative to eachother, a force generated from the conductor bars and a force generatedby the permanent magnets will be counteracted with each other and,therefore, no efficient rotatory drive will be achieved. Also, thepermanent magnet motor provided with such a cage conductor requires acomplicated and increased number of manufacturing steps since thepermanent magnets and the conductor bars are provided in the rotor.

In view of the foregoing, the present invention is intended to solvethose problems inherent in the prior art permanent magnet synchronousmotor and is to increase the efficiency and simplify the manufacture ofthe synchronous motor of the type employing the permanent magnets.

DISCLOSURE OF INVENTION

To this end, the present invention according to a first aspect thereofprovides a synchronous motor which comprises a stator including a statoriron core having a winding wound therearound, said stator iron corehaving an inner cylindrical surface; a rotor including a rotor iron coreand rotatably accommodated while facing the inner cylindrical surface ofthe stator iron core, said rotor including a plurality of conductor barsaccommodated within corresponding slots defined in an outer peripheralportion of the rotor iron core, said conductor bars having theiropposite ends shortcircuited by respective shortcircuit rings to form astarter squirrel cage conductor, said rotor having a plurality of magnetretaining slots defined therein at a location on an inner side of theconductor bars; and permanent magnets embedded within the magnetretaining holes in the rotor and defining rotor magnetic poles. In thissynchronous motor, the neighboring members of the slots are spaced adistance which is referred to as a slot interval, the slot interval at alocation adjacent one end of rotor magnetic poles being smaller than theslot interval at a location adjacent a center point of the rotormagnetic poles.

According to the first aspect of the present invention, the magneticfluxes emanating from the permanent magnets will hardly leak to theouter peripheral surface of the rotor at a position adjacent oppositeends of the rotor magnetic poles and, instead leak to the outerperipheral surface of the rotor at a position adjacent a center point ofthe rotor magnetic poles. For this reason, the pattern of distributionof the magnetic fluxes in an air gap between the stator and the rotorrepresents a generally trapezoidal or sinusoidal waveform such that ascompared with the rectangular waveform, the amount of change of themagnetic fluxes per unitary time increases and, therefore, the voltageinduced across the winding of the stator can be increased to therebyintensify the rotor magnetic poles. Accordingly, in the practice of thepresent invention, to secure the required induced voltage, neither isthe volume of the permanent magnets increased, nor the permanent magnetshaving a high residual magnetic flux density are required such asrequired in the prior art, thus making it possible to provide ahigh-performance and inexpensive self-starting synchronous motor havinga required out-of-step torque and a high efficiency.

If the slot interval at a location spaced from the center point of therotor magnetic poles in a direction conforming to a direction ofrotation of the rotor is chosen to be greater than the slot interval ata location spaced from the center point of the rotor magnetic poles in adirection counter to the direction of rotation of the rotor, althoughduring a loaded operation the maximum value of a distribution, on therotor surface, of composite magnetic fluxes of the magnetic fluxes fromthe winding of the stator and the magnetic fluxes from the permanentmagnets is positioned on one side conforming to the direction ofrotation rather than the center point of the rotor magnetic poles, sincethe slot interval of the rotor through which the magnetic fluxes at thatposition pass is increased, the magnetic saturation at that portion canbe prevented. Accordingly, the magnetic fluxes emanating from themagnets can be sufficiently taken from the rotor and, therefore, thecurrent across the stator winding can be suppressed to thereby increasethe efficiency of the motor.

The present invention according to a second aspect thereof provides asynchronous motor which comprises a stator including a stator iron corehaving a winding wound therearound, said stator iron core having aninner cylindrical surface; a rotor including a rotor iron core androtatably accommodated while facing the inner cylindrical surface of thestator iron core, said rotor including a plurality of conductor barsaccommodated within corresponding slots defined in an outer peripheralportion of the rotor iron core, said conductor bars having theiropposite ends shortcircuited by respective shortcircuit rings to form astarter squirrel cage conductor, said rotor having a plurality of magnetretaining slots defined therein at a location on an inner side of theconductor bars; and permanent magnets embedded within the magnetretaining holes in the rotor and defining rotor magnetic poles. In thissynchronous motor, the slots have a radial length that is smaller at acenter point of the rotor magnetic poles, and a distance between one ofthe slots positioned adjacent one end of the rotor magnetic poles andthe magnet retaining holes is smaller than a distance between the slotspositioned at other locations of the rotor and the magnet retainingholes.

According to the second aspect of the present invention, the magneticfluxes emanating from the permanent magnets will hardly leak to theouter peripheral surface of the rotor at a position adjacent oppositeends of the rotor magnetic poles and, instead leak to the outerperipheral surface of the rotor at a position adjacent a center point ofthe rotor magnetic poles. For this reason, the pattern of distributionof the magnetic fluxes in an air gap between the stator and the rotorrepresents a generally trapezoidal or sinusoidal waveform such that ascompared with the rectangular waveform, the amount of change of themagnetic fluxes per unitary time increases and, therefore, the voltageinduced across the winding of the stator can be increased to therebyintensity the rotor magnetic poles. Accordingly, in the practice of thepresent invention, to secure the required induced voltage, neither isthe volume of the permanent magnets increased, nor the permanent magnetshaving a high residual magnetic flux density are required such asrequired in the prior art, thus making it possible to provide ahigh-performance and inexpensive self-starting synchronous motor havinga required out-of-step torque and a high efficiency.

Preferably, the distance between the slots in the rotor iron core andthe magnet retaining holes progressively increases from a positionadjacent one end of the rotor magnetic poles towards a position adjacentthe center point of the rotor magnetic poles.

The present invention according to a third aspect thereof provides asynchronous motor which comprises a stator including a stator iron corehaving two-pole windings wound therearound, said stator iron core havingan inner cylindrical surface; a rotor including a rotor iron core androtatably accommodated while facing the inner cylindrical surface of thestator iron core, said rotor including a plurality of conductor barspositioned adjacent an outer periphery of the rotor iron core, andshortcircuit rings positioned at axially opposite ends of the rotor ironcore, said conductor bars and shortcircuit rings being integrally moldedtogether by means of an aluminum die casting to form a starter squirrelcage conductor, said rotor having a plurality of magnet retaining slotsdefined therein at a location on the inner side of the conductor bars;and permanent magnets embedded within the magnet retaining holes in therotor and defining two magnetic poles of different polarities. In thissynchronous motor, the shortcircuit rings have an inner diameterpositioned outside the associated magnet retaining holes, the innerdiameter of the shortcircuit rings at a location adjacent one end of themagnetic poles being chosen to be greater than an inner diametricdimension at a location adjacent the center point of the magnetic poles.

According to this structure, the width of the permanent magnets can beincreased and, therefore, with no need to increase the axial length ofthe permanent magnets, the requires area of surface of the magneticpoles of the permanent magnets can be secured. Accordingly, there is noneed to laminate thickness of the rotor iron core, thereby decreasingthe cost.

The inner diameter of the shortcircuit rings on one side where thepermanent magnets are inserted may lie outside the magnet retainingholes in the rotor iron core, in which case the inner diametricdimension of one of the shortcircuit rings adjacent one end of themagnetic poles is chosen to be greater than the inner diametricdimension thereof adjacent the center point of the magnetic poles, andthe inner diametric dimension of the other of the shortcircuit ringslies inwardly of the whole or a part of the magnet retaining holes. Inthis structure, an end plate made of a non-magnetizable plate ispreferably positioned between such other shortcircuit ring and the rotoriron core so as to cover the magnet retaining holes.

This is particularly advantageous in that not only is there no need toincrease the laminate thickness of the rotor iron, but also thecross-section of the other shortcircuit ring is increased to reduce theresistance, and therefore, the number of revolution of the motor at thetime of a maximum torque can increase during a period the motorsubsequent to the start thereof attains a synchronous speed, therebyincreasing the starting performance of the motor.

Also preferably, the inner diameter of the shortcircuit rings on oneside where the permanent magnets are inserted lies outside the magnetretaining holes in the rotor iron core, and the inner diametricdimension of one of the shortcircuit rings adjacent one end of themagnetic poles is chosen to be greater than the inner diametricdimension thereof adjacent the center point of the magnetic poles,whereas the inner diametric dimension of the other of the shortcircuitrings lies inwardly of the whole or a part of the magnet retainingholes. In such case, however, one or a plurality of electromagneticsteel plates of the rotor iron core adjacent the other shortcircuit ringis or are not formed with the magnet retaining holes.

The inner diameter of the shortcircuit rings on one side where thepermanent magnets are inserted may be of a shape lying along the magnetretaining holes in the rotor iron core.

Where the stator iron core is made up of a stator laminate ofelectromagnetic steel plates and the rotor iron core is also made up ofa rotor laminate of electromagnetic steel plates, the stator laminatehas a thickness about equal to that of the rotor laminate.

The present invention in a fourth aspect thereof provides a synchronousmotor which comprises a stator including a stator iron core having awinding wound therearound and also having an inner cylindrical surface;a rotor including a rotor iron core in the form of a rotor laminate of aplurality of electromagnetic steel plates and rotatably accommodatedwhile facing the inner cylindrical surface of the stator iron core, saidrotor iron core including a magnet retaining portion provided withmagnet retaining slots, a magnetic flux shortcircuit preventive portioncoupled with the magnet retaining portion and provided with magneticflux shortcircuit preventive holes communicated with the magnetretaining holes, and a rotor outer end portion coupled with the magneticflux shortcircuit preventive portion and provided with holescommunicated with the magnetic flux shortcircuit preventive holes; andpermanent magnets embedded within the magnet retaining holes in therotor and defining rotor magnetic poles. In this structure, the magneticflux shortcircuit preventive holes are smaller than the magnet retainingholes such that by allowing the permanent magnets to be held inengagement with outer edges of the magnetic flux shortcircuit preventiveholes, the permanent magnets are axially positioned.

This structure is advantageous in that the axial position of thepermanent magnets can be determined relying only on the rotor iron coreand, accordingly, the cost required for assemblage and component partscan be reduced.

The present invention in a fifth aspect thereof provides a synchronousmotor which comprises a stator including a stator iron core having awinding wound therearound, said stator iron core having an innercylindrical surface; a rotor including a rotor iron core in the form ofa rotor laminate of a plurality of iron plates and rotatablyaccommodated while facing the inner cylindrical surface of the statoriron core, said rotor iron core including a magnet retaining portionprovided with magnet retaining slots, and a permanent magnet supportportion coupled with the magnet retaining portion and closing the magnetretaining holes; and permanent magnets embedded within the magnetretaining holes, in the rotor and defining rotor magnetic poles. Thepermanent magnets being axially positioned by means of the permanentmagnet support portion.

This structure is advantageous in that the axial position of thepermanent magnets can be determined relying only on the rotor iron coreand, since one ends of the magnet retaining holes can be closed by therotor iron plate, closure of the magnet retaining hole by means of theend plate secured to the opposite ends of the magnet retaining holes iseffective to permit the use of only one end plate to close the oppositeends of the magnet retaining holes.

An outer end of the rotor iron core may be coupled with the permanentmagnet support portion and provided with hole positioned axially of themagnet retaining holes. In this case, the magnetic resistance of amagnetic circuit between the N and S poles at the axially opposite endsof the permanent magnets can be increased to reduce the leakage of themagnetic fluxes, resulting in increase of the motor characteristic.

Preferably, a starter squirrel cage conductor in the rotor iron core maybe employed in the synchronous motor according to the fifth aspect ofthe present invention.

The present invention in a sixth aspect thereof provides a synchronousmotor which comprises a stator including a stator iron core having awinding wound therearound, said stator iron core having an innercylindrical surface; a rotor including a rotor iron core and rotatablyaccommodated while facing the inner cylindrical surface of the statoriron core, said rotor including a plurality of conductor bars positionedadjacent an outer periphery of the rotor iron core and shortcircuitrings positioned at axially opposite ends of the rotor iron core, saidconductor bars and said shortcircuit rings being integrally moldedtogether by means of an aluminum die casting to form a starter squirrelcage conductor, said rotor iron core having a plurality of magnetretaining holes defined therein; and permanent magnets embedded withinthe magnet retaining holes at a location on the inner side of theconductor bars, said magnet retaining holes having a width in a radialdirection of the rotor iron core being greater at a location inwardly ofan axial direction of the rotor than at a location adjacent one end ofthe axial direction of the rotor.

According to this structure, even though shrinkage stresses generated asthe shortcircuit rings after the aluminum die casting cools whileundergoing shrinkage act on the ends of the rotor iron core, the gapbetween the permanent magnets and the magnet retaining holes can bemaintained at a proper value and, therefore, the insertion of thepermanent magnets into the magnet retaining holes can easily beattained, thereby securing a high-performance motor characteristics.

Where the width of the magnet retaining holes in the radial direction issmaller at opposite ends of the axial direction of the rotor than at alocation inwardly of the axial direction of the rotor and furthercomprising an electromagnetic steel plate provided outside one of theopposite ends of the axial direction of the rotor for closing the magnetretaining holes, the use of only one end plate is sufficient and,therefore, the cost required for the end plate and the number ofassembling steps can advantageously be reduced.

Also, where the width of the magnet retaining holes in the radialdirection is greater at one of opposite ends of the axial direction ofthe rotor than at a location inwardly of the axial direction of therotor and wherein the other of the opposite ends of the axial directionof the rotor is not provided with any magnet retaining holes for closingthe magnet retaining holes at a location inwardly of the axial directionof the rotor, not only is the use of only one end plate sufficient, butalso the number of combinations of the electromagnetic steel plates isminimized to form the rotor iron core, thereby facilitating manufactureof the motor having a high-performance.

The present invention in a seventh aspect thereof provides a synchronousmotor which comprises a stator including a stator iron core having awinding wound therearound, said stator iron core having an innercylindrical surface; a rotor including a rotor iron core and rotatablyaccommodated while facing the inner cylindrical surface of the statoriron core, said rotor including a plurality of conductor bars positionedadjacent an outer periphery of the rotor iron core and shortcircuitrings positioned at axially opposite ends of the rotor iron core, saidconductor bars and said shortcircuit rings being integrally moldedtogether by means of an aluminum die casting to form a starter squirrelcage conductor, said rotor iron core having a plurality of magnetretaining holes defined therein; and permanent magnets embedded withinthe magnet retaining holes at a location on the inner side of theconductor bars. The rotor iron core employed is in the form of alaminate of electromagnetic steel plates and including an entwiningportion provided adjacent the magnet retaining holes for lamination ofthe electromagnetic steel plates, and the magnet retaining holesadjacent the entwining portion has a width in a radial direction thereofwhich is partially enlarged in a direction towards the entwiningportion.

According to this structure, even though when the entwining portion isformed by the use of any known press work, portions of theelectromagnetic steel plates adjacent the entwining portion protrudeunder the influence of press stresses, the gap between the permanentmagnets and the magnet retaining holes can be maintained at a propervalue to thereby facilitate insertion of the permanent magnets and alsoto provide a high-performance motor characteristic.

The present invention in an eight aspect thereof provides a synchronousmotor which comprises a stator including a stator iron core having awinding wound therearound, said stator iron core having an innercylindrical surface; a rotor including a rotor iron core and rotatablyaccommodated while facing the inner cylindrical surface of the statoriron core, said rotor including a plurality of conductor bars positionedadjacent an outer periphery of the rotor iron core and shortcircuitrings positioned at axially opposite ends of the rotor iron core, saidconductor bars and said shortcircuit rings being integrally moldedtogether by means of an aluminum die casting to form a starter squirrelcage conductor, said rotor iron core having a plurality of magnetretaining holes defined therein; and permanent magnets embedded withinthe magnet retaining holes at a location on the inner side of theconductor bars. The rotor iron core has conductor bar holes definedtherein in an axial direction thereof and positioned inwardly of themagnet retaining holes, and the conductor bar holes are filled up by thealuminum die casting simultaneously with the starter squirrel cageconductor. The conductor bars so filled protrude a distance outwardlyfrom an axial end of the rotor iron core to form respective projectionsfor securement of an end plate. The end plate is made of anon-magnetizable material and secured fixedly to the end of the rotoriron core.

This structure is effective in that after the starter squirrel cageconductor and the projections for securement of the end plate have beenformed simultaneously by the use of the aluminum die casting technique,engaging the projections into the engagement holes in the end plate andstaking or crimping respective tips of the projections result in firmconnection of the end plate to the end face of the rotor iron core and,therefore, with no need to employ any bolts, the end plate can easily besecured to the end of the rotor iron core. This permits reduction incost for material and facilitates assemblage of the motor.

The end plate disposed at the axial end of the rotor iron core may bepartly or wholly covered by the corresponding shortcircuit ring, inwhich case a job of connecting the end plate to the end face of therotor iron core is sufficient at only one side of the rotor iron core.

The end plate covered by the shortcircuit ring may be provided withprojections engageable in respective holes in the rotor iron core, sothat positioning of the end plate can easily be performed and, also, thepossibility can be eliminated-which the end plate may displace from theright position under the influence of flow of a high-pressure aluminummelt during the aluminum die casting.

Also, one or a plurality of electromagnetic steel plates at one axialend of the rotor iron core may not be provided with any magnet retaininghole, in which case only one end plate is sufficient at the oppositeaxial end of the rotor iron core, thereby reducing the cost for materialand the number of assembling steps.

In addition, projections may be provided at a location where theelectromagnetic steel plates not provided with any magnet retainingholes contact the permanent magnets, so as to protrude towards thepermanent magnets. In this case, the permanent magnets can be axiallypositioned upon engagement only with the projections and, therefore, themagnetic flux shortcircuit between the different poles of the permanentmagnets through the electromagnetic steel plates can be reducedconsiderably, thereby increasing the performance of the motor.

The present invention in a ninth aspect thereof provides a synchronousmotor which comprises a stator including a stator iron core having awinding wound therearound, said stator iron core having an innercylindrical surface; a rotor including a rotor iron core and rotatablyaccommodated while facing the inner cylindrical surface of the statoriron core, said rotor including a plurality of conductor bars positionedadjacent an outer periphery of the rotor iron core and shortcircuitrings positioned at axially opposite ends of the rotor iron core, saidconductor bars and said shortcircuit rings being integrally moldedtogether by means of an aluminum die casting to form a starter squirrelcage conductor, said rotor iron core having a plurality of magnetretaining holes defined therein, one of the shortcircuit rings having aninner periphery formed with recesses; permanent magnets embedded withinthe magnet retaining holes at a location on the inner side of theconductor bars; and an end plate made of a non-magnetizable material andhaving an outer periphery formed with projections complemental in shapeto the recesses in the shortcircuit ring, a peripheral portion of eachof the recesses in the shortcircuit ring being axially pressed to deformto thereby secure the end plate to an axial end of the rotor iron corewith the projections in the end plate received in the correspondingrecesses in the shortcircuit ring.

Thus, after the end plate can be mounted on the shortcircuit rings withthe projections aligned with and received in the corresponding recess inthe shortcircuit rings, pressing the respective peripheral portions ofthe recesses in the shortcircuit rings to deform results in fixing ofthe end plate to the end face of the rotor iron core, therebyfacilitating the fitting of the end plate.

The present invention according to a tenth aspect thereof provides asynchronous motor which comprises a stator including a stator iron corehaving a winding wound therearound, said stator iron core having aninner cylindrical surface; a rotor including a rotor iron core androtatably accommodated while facing the inner cylindrical surface of thestator iron core, said rotor including a plurality of conductor barspositioned adjacent an outer periphery of the rotor iron core andshortcircuit rings positioned at axially opposite ends of the rotor ironcore, said conductor bars and said shortcircuit rings being integrallymolded together by means of an aluminum die casting to form a startersquirrel cage conductor, said rotor iron core having a plurality ofmagnet retaining holes defined therein, one of the shortcircuit ringshaving an inner periphery formed with recesses; permanent magnetsembedded within the magnet retaining holes at a location on the innerside of the conductor bars; said magnet retaining holes being of adesign allowing the permanent magnets, when embedded therein so as to bebutted end-to-end in a generally V-shaped configuration to form a singlemagnetic pole, and having an air space defined between one end face ofthe permanent magnet and an inner face of one end of the magnetretaining hole for preventing shortcircuit of magnetic fluxes, a barrierslot for preventing shortcircuit of magnetic fluxes being definedbetween the magnet retaining holes for accommodating the neighboringpermanent magnets of different polarities, a first bridge portion beingprovided between the magnet retaining hole and the barrier slot so as tosandwich the barrier slot, and a second bridge portion being providedbetween the neighboring permanent magnets of the same polarity and thecorresponding magnet retaining holes, said second bridge portion beingnarrow at a location adjacent a center of the rotor and large at alocation adjacent an outer periphery of the rotor.

This structure is effective not only to avoid shortcircuit of themagnetic fluxes between the different poles at the end faces of thepermanent magnets to thereby increase the motor performance, but also toreduce the shrinkage strain of the rotor iron core outer diameter at thecenter of the rotor magnetic poles, that have resulted from shrinkage ofthe shortcircuit rings in a radial direction thereof after the aluminumdie casting, to a very small value because of the strength of the bridgeportion having been-increased. Therefore, the gap size between thestator iron core inner diameter and the rotor iron core outer diametercan be accurately obtained merely by blanking the electromagnetic steelplates for the rotor iron core by the use of any known press work andthe outer diameter of the rotor iron core need not be ground, therebyreducing the number of assembling steps.

The present invention according to an eleventh aspect thereof provides asynchronous motor which comprises a stator including a stator iron corehaving a winding wound therearound, said stator iron core having aninner cylindrical surface; a rotor including a rotor iron core androtatably accommodated while facing the inner cylindrical surface of thestator iron core, said rotor including a plurality of conductor barspositioned adjacent an outer periphery of the rotor iron core andshortcircuit rings positioned at axially opposite ends of the rotor ironcore, said conductor bars and said shortcircuit rings being integrallymolded together by means of an aluminum die casting to form a startersquirrel cage conductor, said rotor iron core having a plurality ofmagnet retaining holes defined therein, one of the shortcircuit ringshaving an inner periphery formed with recesses; permanent magnetsembedded within the magnet retaining holes at a location on the innerside of the conductor bars to provide two magnetic poles; said rotoriron core increasing from axially opposite ends thereof towards a centerpoint of the length of the rotor to render it to represent a generallyoval shape, the permanent magnets being mounted after formation of thestarter squirrel cage conductor by means of the aluminum die casting.

According to this structure, even if the shrinkage strain of the rotoriron core outer diameter in a radial direction increases towards thecenter of the rotor magnetic poles after the aluminum die casting, theouter diameter of the rotor iron core after shrinkage can be kept to theright round shape and, therefore, the gap size between the stator ironcore inner diameter and the rotor iron core outer diameter can beaccurately obtained merely by blanking the electromagnetic steel platesfor the rotor iron core by the use of any known press work and the outerdiameter of the rotor iron core need not be ground, thereby reducing thenumber of assembling steps. Also, since the aluminum die casting isperformed while the permanent magnets and the end plates have not yetbeen fitted, the job can easily be performed without incurring anydefective component parts, thereby increasing the productivity.

Where the permanent magnets are employed in the form of a rare earthmagnet, a strong magnetic force can be obtained and both the rotor andthe motor itself can advantageously manufactured in a compact size andlightweight.

BRIEF DESCRIPTION OF DRAWINGS

The present invention will become readily understood from the followingdescription of preferred embodiments thereof made with reference to theaccompanying drawings, in which like parts are designated by likereference numerals and in which:

FIG. 1 is a transverse sectional view of a rotor used in a synchronousmotor according to a first preferred embodiment of the presentinvention;

FIG. 2 is a chart showing a pattern of distribution of magnetic fluxdensities in a gap between a stator and the rotor;

FIG. 3 is a transverse sectional view of the rotor used in thesynchronous motor according to a second preferred embodiment of thepresent invention;

FIG. 4 is a transverse sectional view of the rotor used in thesynchronous motor according to a third preferred embodiment of thepresent invention;

FIG. 5 is a transverse sectional view of the rotor used in thesynchronous motor according to a fourth preferred embodiment of thepresent invention;

FIG. 6 is a transverse sectional view of the rotor used in the prior artself-starting synchronous motor of a kind utilizing permanent magnets;

FIG. 7 is a chart showing the prior art self-starting synchronous motorexhibiting a pattern of distribution of magnetic flux densities in thegap between the stator and the rotor, which pattern represents arectangular waveform;

FIG. 8 is a chart showing the magnetic flux density distribution patternrepresenting a generally trapezoidal waveform;

FIG. 9 is a chart showing the relation between the magnetic flux amountand time that is exhibited when the magnetic flux density distributionpattern represents the rectangular waveform;

FIG. 10 is a chart showing the relation between the magnetic flux amountand time that is exhibited when the magnetic flux density distributionpattern represents the trapezoidal waveform;

FIG. 11 is a chart showing the relation between the induced voltage andtime that is exhibited when the magnetic flux density distributionpattern represents the rectangular waveform;

FIG. 12 is a chart showing the relation between the induced voltage andtime that is exhibited when the magnetic flux density distributionpattern represents the trapezoidal waveform;

FIG. 13 is a chart showing the induced voltage versus angle α that isexhibited when the magnetic flux density distribution pattern representsthe trapezoidal waveform;

FIG. 14 is a longitudinal sectional view of a self-starting synchronousmotor of a type-utilizing permanent magnets according to a fifthpreferred embodiment of the present invention;

FIG. 15 is a transverse sectional view of the rotor used in thesynchronous motor shown in FIG. 14;

FIG. 16 is a plan view of an end plate of the rotor;

FIG. 17 is an end view of the rotor;

FIG. 18 is a longitudinal sectional view of the self-starting permanentmagnet synchronous motor according to a sixth preferred embodiment ofthe present invention;

FIG. 19 is an end view of the rotor used in the synchronous motor ofFIG. 18;

FIG. 20 is a longitudinal sectional view of the self-starting permanentmagnet synchronous motor according to a seventh preferred embodiment ofthe present invention;

FIG. 21 is an end view of an electromagnetic steel plate at one end of arotor iron core employed in the synchronous motor of FIG. 20;

FIG. 22 is an end view of the rotor used in the synchronous motor ofFIG. 20;

FIG. 23 is an end view of the rotor used in the self-starting permanentmagnet synchronous motor according to an eighth preferred embodiment ofthe present invention;

FIG. 24 is a longitudinal sectional view of the self-starting permanentmagnet synchronous motor according to a ninth preferred embodiment ofthe present invention;

FIG. 25 is a transverse sectional view of the prior art rotor;

FIG. 26 is a longitudinal sectional view of the rotor used in thesynchronous motor according to a tenth preferred embodiment of thepresent invention;

FIG. 27 is a plan view of a rotor iron plate E;

FIG. 28 is a plan view of a rotor iron plate F;

FIG. 29 is a longitudinal sectional view of the rotor used in thesynchronous motor according to an eleventh preferred embodiment of thepresent invention;

FIG. 30 is a plan view of the rotor iron plate G;

FIG. 31 is a longitudinal sectional view of the rotor used in thesynchronous motor according to a twelfth preferred embodiment of thepresent invention;

FIG. 32 is a longitudinal sectional view of the rotor used in thesynchronous motor according to a thirteenth preferred embodiment of thepresent invention;

FIG. 33 is a plan view of the rotor iron plate H;

FIG. 34 is a plan view of the rotor iron plate I;

FIG. 35 is a longitudinal sectional view of the rotor used in theself-starting permanent magnet synchronous motor according to afourteenth preferred embodiment of the present invention;

FIG. 36 is a plan view of the electromagnetic steel plate J in the rotoriron core employed in the synchronous motor of FIG. 35;

FIG. 37 is a plan view of the electromagnetic steel plate K at oppositeends of the rotor iron core employed in the synchronous motor of FIG.35;

FIG. 38 is a longitudinal sectional view of the rotor used in theself-starting synchronous motor of the type employing the permanentmagnets according to a fifteenth preferred embodiment of the presentinvention;

FIG. 39 is a plan view of the electromagnetic steel plate L at one endface of the rotor iron core used in the synchronous motor of FIG. 38;

FIG. 40 is a longitudinal sectional view of the rotor employed in theself-starting permanent magnet synchronous motor according to asixteenth preferred embodiment of the present invention;

FIG. 41 is a longitudinal sectional view of the rotor employed in theself-starting permanent magnet synchronous motor according to aseventeenth preferred embodiment of the present invention;

FIG. 42 is an end view of the synchronous motor shown in FIG. 41;

FIG. 43 is a plan view of the electromagnetic steel plate of the rotorused in the self-starting permanent magnet synchronous motor accordingto an eighteenth preferred embodiment of the present invention;

FIG. 44 is a fragmentary enlarged sectional view of an entwining portionas viewed in a direction conforming to the direction of lamination inthe synchronous motor of FIG. 43;

FIG. 45 is a longitudinal sectional view of the self-starting permanentmagnet synchronous motor according to a nineteenth preferred embodimentof the present invention;

FIG. 46 is a transverse sectional view of the rotor used in thesynchronous motor shown in FIG. 45;

FIG. 47 is a plan view of the end plate used in the synchronous motorshown in FIG. 45;

FIG. 48 is a longitudinal sectional view of the self-starting permanentmagnet synchronous motor according to a twentieth preferred embodimentof the present invention;

FIG. 49 is a plan view of the end plate used in the synchronous motorshown in FIG. 48;

FIG. 50 is a cross-sectional view taken along the line C-C′ in FIG. 49;

FIG. 51 is longitudinal sectional view of the self-starting permanentmagnet synchronous motor according to a twenty-first preferredembodiment of the present invention;

FIG. 52 is a plan view of the electromagnetic steel plate at the end ofthe rotor iron core employed in the synchronous motor shown in FIG. 51;

FIG. 53 is a plan view of the electromagnetic steel plate at the end ofthe rotor iron core employed in the self-starting synchronous motoraccording to a twenty-second preferred embodiment of the presentinvention;

FIG. 54 is a fragmentary enlarged longitudinal sectional view of therotor employed in the synchronous motor shown in FIG. 53;

FIG. 55 is a longitudinal sectional view of the self-starting permanentmagnet synchronous motor according to a twenty-third preferredembodiment of the present invention,

FIG. 56 is a longitudinal sectional view of the synchronous motor beforethe end plate is fixed;

FIG. 57 is an end view of the synchronous motor of FIG. 56;

FIG. 58 is a longitudinal sectional view of the prior art rotor;

FIG. 59 is a cross-sectional view taken along the line A-A′ in FIG. 58;

FIG. 60 is a longitudinal sectional view of the rotor used in theself-starting permanent magnet synchronous motor according to atwenty-fourth preferred embodiment of the present invention,

FIG. 61 is a transverse sectional view of the rotor shown in FIG. 60;

FIG. 62 is a fragmentary enlarged view showing a bridge portion; and

FIG. 63 is a plan view of the electromagnetic steel plate of the rotorused in the self-starting permanent magnet synchronous motor accordingto a twenty-fifth preferred embodiment of the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

First Embodiment (FIGS. 1 and 2)

FIG. 1 illustrates a transverse sectional view of a rotor used in aself-starting synchronous motor of a type utilizing permanent magnetsaccording to a first preferred embodiment of the present invention. Inthis figure, reference numeral 21 represents a rotor, and referencenumeral 22 represents a rotor iron core. The rotor iron core 22 has aplurality of slots 23 defined in an outer peripheral portion thereof foraccommodating a corresponding number of conductor bars 24, which areintegrally molded together with shortcircuit rings (not shown) ataxially spaced opposite ends of the rotor iron core 22 by the use of anyknown aluminum die casting to thereby provide a starter squirrel cageconductor. Permanent magnets 26 are embedded in respective magnetretaining holes defined in the rotor iron core 23 at a location radiallyinwardly of a round row of the conductor bars 24.

So far shown in FIG. 1, two plate-like permanent magnets 26 are buttedend-to-end in a generally V-shaped configuration to form a single rotormagnetic pole and, since four permanent magnets are employed in therotor, two rotor magnetic poles are formed. Reference characters T2 andT3 represents the interval between the neighboring slots 23 positionedadjacent the rotor magnetic poles defined by the permanent magnets, andreference character T4 represents the interval between the neighboringslots 23 positioned adjacent a center point between the rotor magneticpoles. In the illustrated embodiment, the intervals T2 and T3 are chosento be smaller than the interval T4.

FIG. 2 is a chart showing a pattern of distribution of magnetic fluxdensities in an air gap between the rotor and the stator, wherein theaxis of ordinates represents the magnetic flux density B and the axis ofabscissas represents the angle θ of the air gap in a directionconforming to the direction of rotation of the rotor with the originrepresented by the center point between the rotor magnetic pole. Sinceat a position adjacent the ends of the rotor magnetic poles theintervals T2 and T3 are smaller than the interval T4 at the centerpoints of the rotor magnetic poles, magnetic fluxes emanating from thepermanent magnets 26 do hardly leak to the outer peripheral surface ofthe rotor 21 and, instead, leak to the outer peripheral surface adjacentthe center points of the rotor magnetic poles. For this reason, thepattern of distribution of the magnetic flux densities in the air gapbetween the stator and the rotor 21 represents a generally trapezoidalwaveform or a generally sinusoidal waveform and, since as compared witha rectangular waveform the amount of change of the magnetic fluxes perunitary time increases, it is possible to increase the voltage inducedacross the winding of the stator.

In contrast thereto, in the prior art self-starting permanent magnetsynchronous motor, the slots in the rotor iron core arecircumferentially spaced at regular intervals and have the same radiallengths as measured in a direction radially of the rotor iron core and,therefore, the pattern of distribution of the magnetic flux densitiestends to represents a rectangular waveform. In general, the intensity ofthe rotor magnetic poles brought about by the permanent magnets can berelatively grasped by measuring the magnitude of the voltage inducedacross the winding of the stator when the rotor is externally rotatedwhile no voltage is applied to the motor.

The relation between the shape of the pattern of distribution of themagnetic flux densities in the air gap between the stator and the rotorand the voltage induced across the stator winding by the action of therotor magnetic poles will now be discussed as applied to the two-poleself-starting motor of the type utilizing the permanent magnets.

The case in which the pattern Bg(θ) of distribution of the magnetic fluxdensities in the air gap represents a rectangular waveform Bg1(θ) isshown in FIG. 7, and the case In which the pattern of distribution ofthe magnetic flux densities in the air gap represents a generallytrapezoidal waveform Bg2(θ) is shown in FIG. 8. The axis of abscissasrepresents the angle θ of the air gap in a direction conforming to thedirection of rotation with the point of origin represented by the centerpoint between the rotor magnetic poles. In FIG. 7, Bg1m represents amaximum value of Bg1(θ) that can be expressed by the followingequations:Bg 1(θ)=Bg 1 m(when 0≦θ≦π)  (1)Bg 1(θ)=−Bg 1 m(when π≦θ≦2)  (2)

In FIG. 8, Bg2m represents a maximum value of Bg2(θ) that can beexpressed by the following equations if the angle α of inclination ofBg2(θ) from θ=0.Bg 2(θ)=θtan α (when 0≦θ≦Bg 2 m/tan−α)  (3)Bg 2(θ)=Bg 2 m (when Bg 2 m/tan α≦θ≦π−B 2 m/tanα)  (4)B 2(θ)=−θtanα+πtan α(when π−Bg 2 m/tanα≦θ≦π)  (5)

It is assumed that the magnetic fluxes of the permanent magnets will norbe shortcircuited within the rotor and are all flow through the statoriron core. Accordingly, regardless of the shape of the waveform of thepattern of distribution of the magnetic flux densities the air gap theamount of the magnetic fluxes flowing in the stator is constant and thearea of surface of the waveform for each magnetic pole remains the sameas can be expressed by the following equation:B _(g1m) π=B _(g2m)[π−(B _(g2m)/tanα)]  (6)

Although the stator winding is distributed over a region correspondingto one magnetic pole, the stator winding can be arranged intensively ina width of an angle π in a direction conforming to the direction ofrotation corresponding to the single magnetic pole and the number ofturns thereof assumed to be n. The amount of the magnetic fluxes φpassing through the winding during rotation of the rotor magnetic polesat an angular velocity w(t) can be expressed by the following equation:$\begin{matrix}{{\phi(t)} = {\int_{\omega\quad t}^{{\omega\quad t} + \pi}{{B_{g}(\theta)}{\mathbb{d}\theta}}}} & (7)\end{matrix}$

The amount of the magnetic fluxes φ1(t) in the case where the patternBg(θ) of distribution of the magnetic flux densities in the air gaprepresents the rectangular waveform Bg1(θ) represents such a waveform asshown in FIG. 9 when Bg1(θ) of each of the equations (1) and (2) issubstituted for Bg(θ) in the equation (7). The amount of the magneticfluxed φ2(t) in the case of the trapezoidal waveform Bg2(θ) representssuch a waveform as shown in FIG. 10 when Bg1(θ) in each of the equations(4) and (5) is substituted for Bg(θ) in the equation (7). The axis ofordinates and the axis of abscissas in each of FIGS. 9 and 10 representthe amount of the magnetic fluxes φ and the time t, respectively.

The waveform V(t) of the voltage induced across the stator winding canbe expressed by the following equation: $\begin{matrix}{{V(t)} = {{{- n}\frac{\mathbb{d}}{\mathbb{d}t}{\int_{\omega\quad t}^{{\omega\quad t} + \pi}{{B_{g}(\theta)}{\mathbb{d}\theta}}}} = {{- \omega}\quad{n\left\lbrack {{B\left( {\theta + \pi} \right)} - {B(\theta)}} \right\rbrack}}}} & (8)\end{matrix}$

The waveform V1(t) of the induced voltage in the case where the patternof distribution of the magnetic flux densities in the air gap representsthe rectangular waveform Bg1(θ) and the waveform V2(t) of the inducedvoltage in the case where the pattern of distribution of the magneticflux densities in the air gap represents the trapezoidal waveform Bg2(θ)are shown in FIGS. 11 and 12, respectively, in which the axis ofordinates represents the induced voltage V(t) and the axis of abscissasrepresents the time t.

The induced voltage V means an effective value of the induced voltagewaveform and is expressed by the following equation: $\begin{matrix}{V = \sqrt{\frac{1}{\pi}{\int_{0}^{\pi}{{V^{2}(t)}{\mathbb{d}t}}}}} & (9)\end{matrix}$

Substituting the equation (8) for the equation (9) results in theinduced voltage V that is expressed by the following equation (10):$\begin{matrix}{V = \sqrt{\frac{\omega^{2}n^{2}}{\pi}{\int_{0}^{\pi}{\left\lbrack {{B\left( {\theta + \pi} \right)} - {B(\theta)}} \right\rbrack^{2}{\mathbb{d}\theta}}}}} & (10)\end{matrix}$

The induced voltage V₁ in the case where the pattern of distribution ofthe magnetic flux densities in the air gap represents the rectangularwaveform Bg1(θ) can be expressed by the following equation bysubstituting the equations (1) and (2) for the equation (10):$\begin{matrix}{V_{1} = {2\omega\quad n\quad B_{g2m}\sqrt{1 - \frac{4B_{g2m}}{3{\pi tan}\quad\alpha}}}} & (11)\end{matrix}$

The induced voltage V₂ in the case where the pattern of distribution ofthe magnetic flux densities in the air gap represents the trapezoidalwaveform Bg2(θ) can be expressed by the following equation bysubstituting the equations (3) and (4) for the equation (10):$\begin{matrix}{V_{2} = {2\omega\quad n\quad B_{g2m}\sqrt{1 - \frac{4B_{g2m}}{3{\pi tan}\quad\alpha}}}} & (12)\end{matrix}$

V₂ is a function of the angle α shown in FIG. 8 and is shown in FIG. 13.When α=π/2, V₂ takes the same value as the equation (11) and it may besaid that when α=π/2 in FIG. 13 the pattern of distribution of themagnetic flux densities in the air gap represents the induced voltage ofthe rectangular waveform. From FIG. 8, since the a is smaller than π/2where the pattern of distribution of the magnetic flux densities in theair gap represents the trapezoidal waveform, it will readily be seenfrom FIG. 13 that the induced voltage where the pattern of distributionof the magnetic flux densities in the air gap represents the rectangularwaveform is lower than that where the pattern of distribution of themagnetic flux densities represents the trapezoidal waveform.

The induced voltage where the pattern of distribution of the magneticflux densities represents the sinusoidal waveform can be similarlyexpressed by the equation (9), and it can be said that the inducedvoltage where the pattern of distribution of the magnetic flux densitiesin the air gap represents the rectangular waveform is lower than thatwhere the pattern of distribution of the magnetic flux densitiesrepresents the sinusoidal waveform. Accordingly, where the pattern ofdistribution of the magnetic flux densities represents the rectangularwaveform, the out-of-step torque is reduced due to the fact that therotor magnetic poles are weak and the efficiency will decrease becauseof increase of the electric current flowing through the stator winding.Therefore, to secure the required induced voltage, it is necessary toincrease the size of the permanent magnets or to employ permanentmagnets having a high residual magnetic flux density and, therefore,there has been a problem in that the cost for the permanent magnets ishigh, accompanied by increase in cost of the motor.

According to the illustrated embodiment of the present invention,however, the voltage induced across the stator winding can be increasedby rendering the pattern of distribution of the magnetic flux densitiesin the air gap between the stator and the rotor to represent either theapproximately trapezoidal waveform or the approximately sinusoidalwaveform. Therefore, it is possible to provide the high-performance,inexpensive self-starting permanent magnet synchronous motor, with noneed to increase the size of the permanent magnets, nor to employ thepermanent magnets having a high residual magnetic flux density.

It is to be noted that although in the foregoing embodiment reference ismade to the rotor of the synchronous motor employing the two poles, thepresent invention may not be limited thereto and may be equally appliedto the rotor having, for example, four or more magnetic poles. Also,although the permanent magnets have been employed in the plate-likeform, the present invention is not limited thereto and the presentinvention is equally applicable to the rotor employing permanent magnetsof, for example, an arcuate shape or any other suitable shape.

Second Embodiment (FIG. 3)

FIG. 3 illustrates a transverse sectional view of the rotor used in theself-starting permanent magnet synchronous motor according to a secondpreferred embodiment of the present invention. In FIG. 3, the rotor 21is shown as rotating in a direction shown by the arrow. During a loadedoperation, a composite magnetic flux of the magnetic flux emanating fromthe stator winding and the magnetic flux emanating from the permanentmagnets 26 flows in a larger quantity in a portion 29 between theneighboring slots that are located on a leading side offset θ1 angularlyin a direction conforming to the direction of rotation of the rotor,than that flowing in a portion 28 between the neighboring slots that arelocated on a trailing side from the center of the rotor magnetic poleswith respect to the direction of rotation of the rotor. The size of thatportion 29, that is, the spacing T8 between the neighboring slots onrespective sides of that portion 29 is chosen to be larger than thespacing T9 between the neighboring slots on respective sides of thatportion 28 and, therefore, it is possible to avoid magnetic saturationof the iron core at that portion 29 between the neighboring slots tothereby secure a favorable motor characteristic.

Third Embodiment (FIG. 4)

FIG. 4 illustrates a transverse sectional view of the rotor used in theself-starting permanent magnet synchronous motor according to a thirdpreferred embodiment of the present invention. In FIG. 4, one of theslots that is identified by 30 is the slot positioned adjacent thecenter of the rotor magnetic poles, and the slots 31 and 32 arepositioned adjacent one of opposite ends of the rotor magnetic poles.These slots 30, 31 and 32 have different radial lengths H30, H31 andH32, respectively, and the distances Y31 and Y32 between the slot 31 andthe magnet retaining hole 25 and between the slot 32 and the magnetretaining hole 25 are chosen to be so smaller than the distance Y30between the slot 30 and the magnet retaining hole 25 that the magneticfluxes emanating from the permanent magnets will hardly leak to theouter peripheral surface of the rotor adjacent the ends of the rotormagnetic poles and will, instead, leak to the outer peripheral surfaceof the rotor adjacent the center of the rotor magnetic poles. For thisreason, the pattern of distribution of the magnetic flux densities inthe air gap between the stator and the rotor can represent the generallytrapezoidal waveform or the generally sinusoidal waveform and, since theamount of change of the magnetic flux per unitary time is so large ascompared with the rectangular waveform, the voltage induced across thestator winding can be increased. Accordingly, with no need to increasethe volume of the permanent magnets or employ the permanent magnetshaving a high residual magnetic flux density in order to secure therequired induced voltage such as implemented in the prior art, it ispossible to provide the high-performance, inexpensive self-startingsynchronous motor of the type employing the permanent magnets that canexhibit a required out-of-step torque and a high efficiency.

Fourth Embodiment (FIG. 5)

FIG. 5 illustrates a transverse sectional view of the rotor used in theself-starting permanent magnet synchronous motor according to a fourthpreferred embodiment of the present invention. In FIG. 5, the slots 33,34, 35, 36, 37, 38 and 39 are those positioned in a region ranging fromthe center to one end of the rotor magnetic poles and are spacedprogressively decreasing distances Y33, Y34, Y35, Y36, Y37, Y38 and Y39,respectively, from the magnet retaining hole 35.

Arrow-headed lines shown in FIG. 5 illustrate the manner in which themagnetic fluxes of the magnetic field formed by the stator winding runacross the rotor 1. For simplification purpose, the pattern of flow ofthe magnetic fluxed is shown only in a lower half of the rotor and notshown in an upper half of the same. As can be seen from this figure, theamount of the magnetic fluxes from the stator is small at a portionbetween the slot 39 adjacent the end of the rotor magnetic poles and themagnet retaining hole, but increases as the center of the magnetic polesapproaches because the magnetic fluxes flowing in between the slotsoverlap. Thus, at a location adjacent the center of the magnetic poles,the amount of the magnetic fluxes is maximized where the magnetic fluxesof the magnetic field developed by the stator winding are intensified.

However, since the distance between each of the slots and the magnetretaining hole as well progressively increases from the end of the rotormagnetic poles towards the center of the rotor magnetic poles, anypossible magnetic saturation of an iron core portion between the slotsand the magnet retaining hole can be prevented, thereby ensuring afavorable motor characteristic.

Fifth Embodiment (FIGS. 4 to 7)

FIG. 14 is a longitudinal sectional view of the self-startingsynchronous motor of a type utilizing permanent magnets according to afifth preferred embodiment of the present invention, and FIG. 15 is across-sectional view taken along the line A-A′ in FIG. 14. FIG. 16 is aplan view of an end plate made of a non-magnetizable material and usedfor protection of the permanent magnets. FIG. 17 is an end view of therotor after the permanent magnets have been inserted and arranged, butbefore the end plate is fixed to the rotor.

In these figures, reference numeral 41 represents a rotor, and referencenumeral 42 represents a rotor iron core in the form of a laminatedstructure of electromagnetic steel plates. Reference numeral 43represents conductor bars molded together with shortcircuit rings 44positioned on respective ends of the conductor bars by means of analuminum die casting technique to provide a starter squirrel cageconductor. Reference numeral 45 represents permanent magnets each havinga width Q. Reference numeral 46 represents magnet retaining holesdefined in the rotor iron core 42 for accommodating therein thepermanent magnets. After the aluminum die casting, two plate-likepermanent magnets 45 of the same polarity are butted end-to-end in agenerally V-shaped configuration to form a single rotor magnetic poleand, since four permanent magnets 45 e employed in the rotor, two rotormagnetic poles are formed.

Reference numeral 47 represents a barrier for preventing a shortcircuitof the magnetic fluxes developed between the neighboring permanentmagnets of different polarities, which is also filled in position bymeans of the aluminum die casting. Reference numeral 48 represents endplates made of a non-magnetizable material and used to protect thepermanent magnets, each being formed with an engagement hole 48 a.Reference numeral 49 represents axial holes defined in the rotor ironcore 42 so as to extend axially thereof, which holes are filled withaluminum 50 that is used during the aluminum die casting to form thestarter squirrel cage conductor. The aluminum 50 filling up the axialhole 49 protrudes axially outwardly from the opposite ends of the rotoriron core 42 to thereby define projections 50 a as best shown in FIG.14. The end plates 48 are, after the projections 50 a have been passedthrough the associated engagement holes 48 a in the end plates 48, fixedto the opposite end faces of the rotor iron core 42 by crimping orstaking the projections 50 a to enlarge as shown by broken lines in FIG.14. Reference numeral 51 represents a bearing hole defined in the rotoriron core 42.

The amount of the magnetic fluxes of the permanent magnets 45 that canbe obtained from the rotor is substantially proportional to the productof the width Q of the permanent magnets 45 times the length of thepermanent magnets 45 as measured in the axial direction of the rotor,that is, the area of magnetic poles of the permanent magnets 45.

It is to be noted that although in the foregoing description thepermanent magnets which have been magnetized are inserted and arranged,the rotor magnetic poles may be equally formed by inserting andarranging permanent magnets, which have not yet been magnetized, in therotor iron core to complete the rotor and then polarizing the permanentmagnets with the use of a magnetizing apparatus.

According to the fifth embodiment of the present invention, the angle βof end-to-end abutment of the same poles of the permanent magnets 45 ischosen to be larger than the angle α in the prior art that is 90° asshown in FIG. 25, and the width Q of each permanent magnet 45 asmeasured in a direction perpendicular to the longitudinal axis thereofis enlarged to a value larger than the width P in the prior art as shownin FIG. 25. Increase of the angle of end-to-end abutment of thepermanent magnets and selection of the inner radial dimension c at alocation adjacent the end of the rotor magnetic poles to be larger thanthe inner radial dimension b at a location adjacent the center of therotor magnetic poles is effective to allow the permanent magnets of theincreased width to be employed. In correspondence with the increase ofthe angle of end-to-end abutment of the permanent magnets 45 andincrease of the width of the permanent magnets 45, each of theshortcircuit rings 44 employed in the present invention is not round inshape such as used in the prior art, but of a generally rhombic shape,as shown in FIG. 14, having its outer contour positioned outwardly ofthe magnet retaining holes 46 and allowing an inner diameter of the endsof the rotor magnetic poles to be greater than that of the center of therotor magnetic poles.

The reason that the inner diameter of each of the shortcircuit rings 44a is not chosen to be round in conformity with the inner diameter at theend of the magnetic poles of the total peripheral rotor is that, if itis so chosen, the equivalent sectional surface area of each shortcircuitring A as a whole of 44 a will become so excessively small as toincrease the resistance, resulting in reduction in starting capabilityof the motor.

As discussed above, according to the fifth embodiment of the presentinvention, since the permanent magnets 45 can have an increased area ofsurface of the magnetic poles, the amount of the magnetic fluxes of thepermanent magnets required by the motor can be obtained.

Sixth Embodiment (FIGS. 18 and 19)

A sixth preferred embodiment of the present invention will now bedescribed with reference to FIGS. 18 and 19., wherein FIG. 18 is alongitudinal sectional view of the self-starting synchronous motor of atype utilizing permanent magnets according to the sixth embodiment ofthe present invention and FIG. 19 is an end view as viewed from an Sside in FIG. 18. In FIG. 19, broken lines show the position of magnetretaining holes 46 and single-dotted lines show an outer contour of theend plate 58. Although an end view of the rotor as viewed from an R sideis not shown, the width and the angle of end-to-end abutments of thepermanent magnets 45 and the inner diametric shape of the shortcircuitring A of 44 a are all similar to those in the previously describedfirst embodiment of the present invention, and the shortcircuit ring Bof 44 b on the opposite S side has an inner diameter that is round andis so chosen to be small as to allow it to be positioned inwardly of themagnet retaining holes 46.

Referring to FIGS. 18 and 19, the end plate 58 is similarly arranged inabutment with an end face of the rotor iron core 42 on the S side and isof a shape sufficient to encompass the magnet retaining holes 46 and,accordingly, there is no possibility that the die cast aluminum may leakinto the magnet retaining holes 46 which would otherwise render itdifficult to insert the permanent magnets 45.

Seventh Embodiment (FIGS. 20 to 22)

A seventh preferred embodiment of the present invention will now bedescribed with reference to FIGS. 20 to 22. FIG. 20 is a longitudinalsectional view of the self-starting synchronous motor of a typeutilizing permanent magnets according to the seventh embodiment of thepresent invention, FIG. 21 is a plan view of one or a plurality ofelectromagnetic steel plates 59 at one end on the S side of the rotoriron core 2, and FIG. 22 is an end view as viewed from the S side.Although an end view of the rotor as viewed from the R side is notshown, the width and the angle of end-to-end abutments of the permanentmagnets 45 and the inner diametric shape of the shortcircuit ring A of44 a are all similar to those in the previously described fifthembodiment of the present invention.

Referring to FIGS. 20 to 22, the shortcircuit ring C of 44 c on the Sside has its inner diameter or bore which is round and is so chosen asto be positioned inwardly of the magnet retaining holes 46. One or aplurality of electromagnetic steel plates 59 at the end on the S side ofthe rotor iron core 42 is provided with slots of the same shape and sizedefined at the same position as the electromagnetic steel plates otherthan those at the end, but no magnetic retaining hole 46 is provided.Accordingly, even though the inner diameter of the shortcircuit ring Cof 44 c is small, there is no possibility that the die cast aluminumwill leak into the magnet retaining holes 46 to render it to bedifficult to insert the permanent magnets.

Eighth Embodiment (FIG. 23)

An eighth embodiment of the present invention will be described withreference to FIG. 23 which is an end view of the rotor as viewed in adirection conforming to the direction of insertion of permanent magnets45, showing the rotor after the permanent magnets 45 have been insertedand arranged, but before the end plate is mounted.

Referring to FIG. 23, the inner diameter or bore of the shortcircuitring D of 44 d is of a shape conforming to and extending along themagnet retaining holes 46. This design permits the permanent magnets 45to be inserted along a wall surface inside the inner diameter or bore ofthe shortcircuit ring D of 44 d, thereby facilitating a job of insertionof the permanent magnets to thereby increase the ease to assembly.

Ninth Embodiment (FIG. 24)

A ninth preferred embodiment of the present invention will be describedwith reference to FIG. 24 and also to FIG. 17 used in connection withthe fifth embodiment of the present invention. FIG. 24 illustrates atransverse sectional view of the self-starting synchronous motor of thetype employing the permanent magnets according to the ninth embodimentof the present invention. In this figure, reference numeral 61represents a stator, and reference numeral 62 represents a stator ironcore in the form of a laminate structure of electromagnetic steelplates, which laminate structure has a laminate thickness indicated byLs. Reference numeral 63 represents a stator winding wound around thestator iron core 62. The rotor 41 employed therein is substantiallyidentical with that described in connection with the fifth embodimentwith reference to FIG. 17 and are not therefore described for the sakeof brevity however, as is the case with the rotor shown in FIG. 17, byincreasing the width of the permanent magnets 45 as measured in adirection perpendicular to the longitudinal axis thereof to therebyincrease the area of surface of the magnetic poles of the permanentmagnets 45 to increase the amount of the magnetic fluxes emanating fromthe permanent magnets 45, and also by designing the inner diameter orbore of the shortcircuit ring A of 44 a to be positioned outwardly ofthe magnet retaining holes 46 and, again by selecting the inner radialdimension adjacent the end of the rotor magnetic poles of theshortcircuit ring A of 44 a to be larger than that adjacent the centerof the rotor magnetic poles, the laminate thickness of theelectromagnetic steel plates forming the rotor iron core 42 canadvantageously reduced to a value substantially equal to the laminatethickness Ls of the stator iron core.

The motor of the type utilizing the permanent magnets is generallydesigned by selecting the axial length of the permanent magnets to begreater than the laminate thickness of the stator iron core so thatportions of the magnetic fluxes of the permanent magnets, which emergeoutwardly from the opposite ends of the stator iron core, can flowinwardly of the stator iron core from the opposite ends thereof tothereby increase the amount of the magnetic fluxes that runs through thewhole of the stator iron core and, for that purpose, the laminatethickness of the rotor iron core is chosen to be greater than thelaminate thickness of the stator iron core. In contrast thereto,according to the ninth embodiment of the present invention, the designhas been employed as hereinabove described to render the laminatethickness Ls of the stator iron core and the laminate thickness L_(R) ofthe rotor iron core to be substantially equal to each other.

In view of the foregoing, the number of the electromagnetic steel platesfor each of the stator and rotor iron cores that are simultaneouslyblanked within the same dies is substantially equal for the both and,therefore, production of surplus electromagnetic steel plates can besuppressed to thereby reduce the cost.

Tenth Embodiment (FIGS. 26 to 28)

A tenth preferred embodiment of the present invention will now bedescribed with reference to FIGS. 26 to 28. FIG. 26 is a longitudinalsectional view of the rotor used in the synchronous motor according tothe tenth embodiment of the present invention. In FIG. 26, referencenumeral 71 represents a rotor, and reference numeral 72 represents arotor iron core. Reference numeral 72 a represents a rotor iron coreformed by laminating rotor iron plates E, and one of the rotor ironplates E is shown in FIG. 27. In FIG. 27, reference numeral 73represents magnet retaining holes, and when the rotor iron plates E arelaminated, the magnet retaining holes 73 are axially aligned with eachother as shown in FIG. 26 with the respective permanent magnets 74subsequently embedded therein.

Reference numeral 72 b 1 shown in FIG. 26 represents a rotor iron coreformed by laminating rotor iron plates F to an axial end face of therotor iron core 72 a, one of the rotor iron plates F being shown in FIG.28 in a plan view. In FIG. 28, reference numeral 77 represents magneticflux shortcircuit preventive holes that are arranged at the sameposition as the magnet retaining holes 73 in the rotor iron plates E,but have a width U smaller than the width T of the magnet retainingholes 73. When the rotor iron plates F are laminated to the axial endface of the rotor iron core 72 a, the magnetic flux shortcircuitpreventive holes 77 are axially communicated with the magnet retainingholes 73 as shown in FIG. 26. In FIG. 26, reference numeral 72 c 1represents a rotor iron core made of one or more rotor iron plates Elaminated to the axial end face of the rotor iron core 72 b 1. Also, inFIG. 26, reference numeral 76 represents an end plate made of anon-magnetizable material and having a shape sufficient to overlay themagnet retaining holes 73 and the magnetic flux shortcircuit preventiveholes 77 so as to prevent debris of the permanent magnets 74, whichwould be generated at the time the permanent magnets 74 are inserted inand embedded in the magnet retaining holes 73, from flowing outwardlyand also to prevent external foreign matter from being trapped into themagnet retaining holes 73.

As shown in FIG. 26, an axial end face 79 of each of the permanentmagnets 79 is held in engagement with an outer peripheral edge 78 of therespective magnetic flux shortcircuit preventive hole 77 on an abutmentface of the rotor iron core 72 b 1 that is in engagement with the rotoriron cores 72 a and, accordingly, magnetic fluxes 80 leaking between Nand S poles at the respective opposite ends of the permanent magnets 74run from the rotor iron cores 72 a back to the permanent magnets 74through the rotor iron core 72 b 1, then across the magnetic fluxshortcircuit preventive holes 77 and finally through the rotor ironcores 72 b 1 and 72 a. The leaking magnetic fluxes 80 b 1 runs from therotor iron cores 72 a back to the permanent magnets 74 through the rotoriron core 72 b 1, then through the rotor iron core 72 c 1, across themagnet retaining holes 73, again through the rotor iron core 72 c 1, therotor iron core 72 b 1 and finally through the rotor iron core 72 a.Where the rotor iron core 72 b 1 is made up of a single rotor iron plateor a plurality of rotor iron plates F in a number as small as possibleso long as the permanent magnets can be positioned, a magnetic circuitthrough which the leaking magnetic fluxes 80 a 1 run can have a magneticresistance of a magnitude sufficient to minimize the leaking magneticfluxes 80 a 1. Also, since the width T of the magnet retaining holes 73in the rotor iron plate E forming the rotor iron core 72 c 1 is solarger than the width U of the magnetic flux shortcircuit preventivehole 77 in the rotor iron plate F that, as compared with the case inwhich the rotor iron core 72 c 1 is prepared from the rotor iron plateF, the magnetic circuit through which the leaking magnetic fluxes 80 b 1run can have a magnetic resistance of a magnitude sufficient to minimizethe leaking magnetic fluxes 80 b 1. Therefore, the motorcharacteristic-can be increased.

Also, since the permanent magnets 74 attracts and is therefore held inengagement with the outer peripheral edge 78 of the magnetic fluxshortcircuit preventive hole 77 in the rotor iron core 72 b 1, thepermanent magnets 74 can be accurately positioned with respect to theaxial direction thereof only by means of the rotor iron cores 72 with noholder employed, thereby reducing the cost for assembly and componentparts.

It is to be noted that the number of the rotor iron plates F laminatedis so chosen that a point intermediate of the axial length of the rotoriron cores 72 can match with a point intermediate of the axial length ofthe permanent magnets 74, and this equally applies to any one of theembodiments of the present invention that follow.

It is also to be noted that where the permanent magnets are made of arare earth metal of, for example, Nd—Fe—B system, since the magnet madeof the rare earth metal of the Nd—Fe—B system is known to exhibit a highresidual magnetic flux density, the volume of the rotor and the motor asa whole can advantageously be reduced.

In describing the tenth embodiment of the present invention, thepermanent magnets has been employed in the form of a generallyplate-like configuration, but the present invention may not be limitedthereto and can be equally applied to the rotor employing the permanentmagnets of any suitable shape such as, for example, an arcuate shape.

Eleventh Embodiment (FIGS. 29 and 30)

An eleventh preferred embodiment of the present invention will bedescribed with reference to FIGS. 29 and 30, wherein FIG. 29 is alongitudinal sectional view of the rotor used in the synchronous motorand FIG. 30 is a plan view of the rotor iron plate G. As shown in FIG.29, reference numeral 72 d 1 represents a rotor iron core comprising arotor iron core 72 a having its axial end face to which rotor ironplates G are laminated. Since the rotor iron plates G have no magnetretaining hole defined therein, lamination of the rotor iron plates G tothe axial end face of the rotor iron core 72 a results closure of themagnet retaining holes 73.

Since the axial end face 81 of the permanent magnets 74 is held inengagement with an abutment face of the rotor iron core 72 d 1 that isheld in engagement with the rotor iron core 72 a, magnetic fluxes 80 c 1leaking from the axial end of the permanent magnets 74 runs from therotor iron core 72 a back to the permanent magnets 74 through the rotoriron core 72 d 1 and then through the rotor iron core 72 a. Also, sincethe permanent magnets 74 attract and are therefore held in engagementwith the axial end face 82 of the rotor iron core 72 d 1, the permanentmagnets 74 can be accurately positioned with respect to the axialdirection thereof with no need to use any holder, thereby reducing thecost for assembly and component parts.

Also, since the magnet retaining holes 73 in the rotor iron core 72 aare closed at one end by the rotor iron core 72 d 1, positioning of asingle end plate 76 at the opposite end is sufficient to close theopposite ends of the magnet retaining holes 73. While in the previouslydescribed tenth embodiment of the present invention, two end plates 76are required, the eleventh embodiment requires the only end plate 6 and,therefore, the cost for assembly and component parts can further bereduced.

The rotor iron plate E and the rotor iron plate G can easilymanufactured by controlling loading and unloading of blanking dies, thatare used to form the magnet retaining hole 73, during a blankingprocess. Therefore, no blanking dies that are required in the previouslydescribed tenth embodiment of the present invention to form the magneticflux shortcircuit preventive hole 77 in the rotor iron plate F isneeded, making it possible to simplify the structure of the diesthemselves.

Twelfth Embodiment (FIG. 31)

FIG. 31 illustrates a longitudinal sectional view of the rotor used inthe synchronous motor according to a twelfth embodiment of the presentinvention. An axial end face of the rotor iron core 72 d 2 opposite tothat with which the axial end face 81 of the permanent magnets 74 areheld in engagement is provided with a rotor iron core 72 c 2 of alaminated structure including rotor iron plates E.

Since the axial end face 81 of the permanent magnet 74 is held inengagement with the axial end face 82 of the rotor iron core 72 d 2,magnetic fluxes 80 c 2 leaking at the axial end of the permanent magnet74 run from the rotor iron core 72 a back to the permanent magnet 74through the rotor iron core 72 d 2 and then through the rotor iron core72 a. The leaking magnetic fluxes 80 b 2 runs from the rotor iron cores72 a back to the permanent magnet 74 through the rotor iron core 72 d 2,then through the rotor iron core 72 c 2, across the magnet retainingholes 73, again through the rotor iron core 72 c 2, the rotor iron core72 d 2 and finally through the rotor iron core 72 a.

Since the leaking magnetic fluxes 80 c 1 traverse the magnet retainingholes 73, as compared with the magnetic resistance of the magneticcircuit through which the leaking magnetic fluxes 80 c 1 run in thepreviously described eleventh embodiment of the present invention, themagnetic circuit through which the leaking magnetic fluxes 80 b 2 run inthis twelfth embodiment has a relatively high magnetic resistance and,therefore, the sum of the leaking magnetic fluxes 80 c 2 and 80 b 2 inthis twelfth embodiment is smaller relative to the leaking magneticfluxes 80 c 1 in the previously described eleventh embodiment.Accordingly, since the leaking magnetic fluxes can be reduced ascompared with that in the previously described embodiment, the motorcharacteristic can be increased.

Thirteenth Embodiment (FIGS. 32 to 34)

A thirteenth preferred embodiment of the present invention will bedescribed with reference to FIGS. 32 to 34. FIG. 32 illustrates alongitudinal sectional view of the rotor used in the synchronous motoraccording to the thirteenth embodiment of the present invention. In thisfigure, reference numeral 83 represents a rotor and reference numeral 84represents a rotor iron core. Reference numeral 84 a represents a rotoriron core made up of a laminate of rotor iron plates H. Referencenumeral 84 b represents a rotor iron core made up of a laminate of rotoriron plates 1, one of which is shown in FIG. 34 in a plan view.

FIG. 33 illustrates a plan view of the rotor iron plate H. In thisfigure, reference numeral 85 represents a plurality of slots foraccommodating conductor bars 86 a of the starter squirrel cageconductor, and reference numeral 73 represents magnet retaining holes.

Referring to FIG. 34, reference numeral 87 represents a plurality ofslots for accommodating the conductor bars 86 a of the starter squirrelcage conductor shown in FIG. 32, which slots 86 a are of the same shapeas the slots 85 in the rotor iron plate H and are positioned at the sameposition as the slots 85 in the rotor iron plate H. Reference numeral 77represents magnetic flux shortcircuit preventive holes that arepositioned at the same position as the magnet retaining holes 73 in therotor iron plate H of FIG. 33, but have a width U smaller than the widthT of the magnet retaining holes 73.

Referring back to FIG. 32, reference numeral 84 c represents a rotoriron core made up of one rotor iron plate E or a laminate of rotor ironplates E. By the use of any known aluminum die casting technique, theconductor bars 86 a and shortcircuit rings 86 b are formed integrallytogether to define the starter squirrel cage conductor. By arranging thestarter squirrel cage conductor in the rotor 83, the self-startingsynchronous motor of the type employing the permanent magnets can beobtained which operates as an inductor motor at the time of startingthereof and as a synchronous motor entrained by a synchronous speed uponarrival at the synchronous speed. Even in this case, since as is thecase with the previously described tenth embodiment of the presentinvention, the rotor iron core 84 b having the magnetic fluxshortcircuit preventive holes 77 defined therein are employed and therotor iron plates E are laminated, the leaking magnetic fluxes betweenthe N and S poles at the axially opposite ends of the permanent magnets74 can be reduced, thereby increasing the motor characteristic.

Even in the self-starting synchronous motor of the type employing thepermanent magnets in which the starter squirrel cage conductor isarranged such as in this thirteenth embodiment, the permanent magnets 74can be accurately positioned only by the rotor iron core 84 with no needto employ any holder and, therefore, the cost for assembly and componentparts can be reduced advantageously.

Fourteenth Embodiment (FIGS. 35 to 37)

A fourteenth preferred embodiment of the present invention will bedescribed with reference to FIGS. 35 to 37, wherein FIG. 35 illustratesa longitudinal sectional view of the rotor used in the synchronous motoraccording to the fourteenth embodiment of the present invention, FIG. 36illustrates a plan view of an electromagnetic steel plate J positionedinwardly of opposite axial ends of the rotor, iron core and FIG. 37illustrates a plan view of an electromagnetic steel plate K positionedat the opposite axial ends of the rotor iron core.

Referring now to FIGS. 35 to 37, reference numeral 91 represents arotor, and reference numeral 92 represents a rotor iron core of alaminated structure including the electromagnetic steel plates J 110 andthe electromagnetic steel plates K 111. The electromagnetic steel platesJ 110 and K 111 are formed with respective conductor bar slots 112 ofthe same size, respective barrier slots 113 of the same size forpreventing the magnetic flux shortcircuit, respective holes 99 of thesame size and respective bearing holes 114 of the same size, which arealigned with each other. Reference numerals 96 b and 96 a representmagnet retaining holes defined at the same position, wherein respectivehole widths R and S as measured in a direction radially thereof are sochosen as to satisfy the relationship R<S.

Reference numeral 93 represents conductor bars made of aluminum andfilled in the respective slots 112. The conductor bars 93 are integrallymolded together with the shortcircuit rings 94 at the axially oppositeends of the rotor iron core 92 by means of any known aluminum diecasting technique to thereby form the starter squirrel cage conductor.Reference numeral 95 represents permanent magnets, every two of whichare, after the aluminum die casting, held in end-to-end abutment torepresent a generally V-shaped configuration and are then inserted andarranged in the magnet retaining holes 96 and 96 a so that the two pairsof the permanent magnets 95 can define two magnetic poles. The barrierslots 113 are filled; up with aluminum injected during the aluminum diecasting to avoid any possible shortcircuit between the neighboringpermanent magnets of the different polarities. Reference numeral 98represents a non-magnetizable end plate for protection of the permanentmagnets 95, which end plate has an engagement hole 98 a defined therein.Reference numeral 99 represents an axial hole defined in the rotor ironcore 92 so as to extend axially thereof, in which hole is filledaluminum 100 that is injected during the aluminum die casting to formthe starter squirrel cage conductor. The aluminum 100 filled in theaxial hole 99 has projections 100 a protruding outwardly from theaxially opposite ends of the rotor iron core 92. The end plates 98 are,after the engagement holes 98 a have received therein the projections100 a, fixed to the respective axial end faces of the rotor iron core 92by staking or crimping the projections 100 a to enlarge as shown bybroken lines. Reference numerals 101 and 114 represents respectivebearing holes.

It is to be noted that although in the foregoing description thepermanent magnets which have been magnetized are inserted and arranged,the rotor magnetic poles may be equally formed by inserting andarranging permanent magnets, which have not yet been magnetized, in therotor iron core to complete the rotor and then polarizing the permanentmagnets with the use of a magnetizing apparatus.

During the manufacture of the self-starting synchronous motor of thestructure described above, and at the time the shortcircuit rings 94formed by the aluminum die casting cool, the outer diameter of themagnet retaining holes 96 a in the electromagnetic steel plates K 111 ateach axial end of the rotor iron core 92 deforms and contracts under theinfluence of a force of shrinkage acting in an inner radial direction.However, since the hole width S of the magnet retaining holes 96 a issufficiently larger than the hole width R of the magnet retaining hole96 in the electromagnetic steel plates J that are small of the shrinkageforce of the shortcircuit rings 94, there is no possibility that as aresult of reduction in gap between the permanent magnets 95 b and themagnet retaining holes 96 a that is brought about by deformation andshrinkage insertion of the permanent magnets 95 into the respectivemagnet retaining holes 96 a is difficult to achieve.

The hole width S of the magnet retaining holes 98 a is so chosen as tobe slightly greater than R by a quantity that a side adjacent an outerdiameter of the hole width S when receiving the shrinkage force of theshortcircuit ring 94 can line up with a side adjacent an outer diameterof the hole width R of the magnet retaining hole 96, and accordingly, apossibility can be avoided which would, as a result of reduction of thecoefficient of permeance of the magnetic circuit can be lowered, themotor characteristic may correspondingly decrease.

As hereinabove described, the self-starting synchronous motor of thetype employing the permanent magnets according to the fourteenthembodiment is advantageous in that the permanent magnets 5 can be easilyinserted subsequent to the aluminum die casting and that ahigh-performance motor characteristic can be maintained.

Fifteenth Embodiment (FIGS. 38 and 39)

A fifteenth preferred embodiment of the present invention will bedescribed with reference to FIGS. 38 and 39 in combination with FIGS. 36and 37. FIG. 38 is-a longitudinal sectional view of the rotor used inthe self-starting synchronous motor of the type employing the permanentmagnets according to the fifteenth preferred embodiment of the presentinvention, and FIG. 39 is a plan view of the electromagnetic steel plateL at one end face of the rotor iron core 92 of FIG. 38.

Referring now to FIGS. 38 and 39, one or a plurality of electromagneticsteel plates L 120 at one end of the rotor iron core on the P side haveno magnet retaining hole defined therein. The electromagnetic steelplates on the axially opposite ends of the rotor iron core 92 arelaminated with the same electromagnetic steel plates K 111 as thoseshown in FIG. 37 in connection with the fourteenth embodiment and theelectromagnetic steel plates J 110 are laminated inwardly of theopposite ends. Since the axial end face of the permanent magnets abutsagainst the electromagnetic steel plate L, the number of theelectromagnetic steel plates L laminated is so chosen that respectiveaxial centers of the rotor iron core and the permanent magnets can matchwith each other.

In the fifteenth embodiment of the present invention which is soconstructed as hereinabove described, since the rotor 91 is such thatone or a plurality of the electromagnetic steel plates L 120 at the endof the rotor iron core 92 on the P side has no magnet retaining holedefined therein, the only end plate 98 is sufficient on the opposite Qside and, therefore, the cost for material and the number of fittingsteps can be reduced advantageously. Also, since the hole width S of themagnet retaining holes 96 a in the electromagnetic steel plates K 111 onthe axially opposite ends of the rotor iron core 2 is sufficientlygreater than the hole width R of the magnet retaining holes 96 in theinside electromagnetic steel plates J 110, even though a radiallyinwardly shrinking deformation occurs under the influence of theradially inwardly acting shrinkage force from the shortcircuit rings 94subsequent to the aluminum die casting, the permanent magnets 95 can becarried out without being disturbed and, since as is the case with thefirst embodiment of the present invention, the gaps between thepermanent magnets 95 b and the magnet retaining holes in the rotor ironcore 92 are properly maintained, a high-performance motor characteristiccan be maintained.

Sixteenth Embodiment (FIG. 40)

A sixteenth preferred embodiment of the present invention will bedescribed with reference to FIG. 40 in combination with FIGS. 36 to 38.FIG. 40 is a longitudinal sectional view of the rotor employed in theself-starting permanent magnet synchronous motor according to thesixteenth embodiment. As shown in FIG. 40, one or a plurality ofelectromagnetic steel plates L 120 shown in FIG. 40 and having no magnetretaining holes defined therein are laminated to one end of the rotoriron core 92 on the P side, and one or a plurality of electromagneticsteel plates K 111 having the magnet retaining holes of a relativelygreat hole width are laminated to the opposite end of the rotor ironcore 92 on the Q side. Since no magnet retaining hole is defined in theelectromagnetic steel plates L 120 on the P side end, the shrinkagestress of the shortcircuit ring 94 has no concern therewith and,therefore, the permanent magnets 95 can easily be inserted in the rotoriron core 92 if the electromagnetic steel plates K 111 having the magnetretaining holes 96 of a relatively great hole width are arranged only onthe Q side. Accordingly, the rotor iron core 92 can be assembled with aminimized combination of the electromagnetic steel plates J 110, K 111and L 120, thereby facilitating the manufacture thereof and alsomaintaining a high-performance motor characteristic.

Seventeenth Embodiment (FIGS. 41 and 42)

A seventeenth preferred embodiment of the present invention will bedescribed with reference to FIGS. 41 and 42 in combination with FIG. 39.FIG. 41 is a longitudinal sectional view of the rotor employed in theself-starting permanent magnet synchronous motor according to theseventeenth embodiment and FIG. 42 is an end view of the synchronousmotor viewed from the P side in FIG. 41.

The basic structure of the rotor in the seventeenth embodiment issubstantially similar to that described in connection with any of thefifteenth and sixteenth embodiments.

Referring to FIGS. 41 and 42, the shortcircuit ring 94 a having areduced inner diameter is formed on an outer end face of theelectromagnetic steel plates L 120 shown in FIG. 39 and having no magnetretaining hole defined therein on the P side, by means of the aluminumdie casting. The inner diameter of the shortcircuit ring 94 a is suchthat it can be enclosed inwardly of the whole of the magnet retainingholes 96 and 96 a defined respectively in the electromagnetic steelplates j and K as shown by the broken lines, or partly inwardly thereofalthough not shown. Since the electromagnetic steel plates L 120 have nomagnet retaining hole such as identified by 96, there is no possibilitythat during the aluminum die casting aluminum may penetrate into themagnet retaining holes 96. In view of the foregoing, the shortcircuitring 94 a can have an increased cross-sectional surface area to therebyreduce a secondary resistance of the rotor, the rotational speed of themotor at the time of a maximum torque en route the synchronous speed andthe at the time of the maximum torque can increase to facilitate asynchronous entanglement, thereby increasing the starting performance ofthe motor.

Eighteenth Embodiment (FIG. 43)

An eighteenth preferred embodiment of the present invention will bedescribed with reference to FIG. 43 which shows a plan view of anelectromagnetic steel plate M for the rotor of the self-startingpermanent magnet synchronous motor according to the eighteenthembodiment.

The basic structure of the rotor in the eighteenth embodiment issubstantially similar to that described in connection with any of theeighteenth and seventeenth embodiments. Referring now to FIG. 43,reference numeral 131 represents entwining portions for lamination ofthe electromagnetic steel plates. As shown in FIG. 43, when theelectromagnetic steel plates are blanked one by one, press projectionsare formed and are laminated together while sequentially entwinedtherewith to thereby form the rotor iron core. In such case, theentwining portions 131 are defined at respective locations outwardly ofthe magnet retaining holes 132. Reference numeral 132 a represents anenlarged portion in which the hole width of a portion of each magnetretaining hole 132 adjacent the corresponding entwining portion 131 isenlarged radially outwardly by a required quantity V towards suchcorresponding entwining portion 131. Reference numeral 133 represents apincer portion of the electromagnetic steel plate M 130 bound betweenthe corresponding entwining portion 131 and the enlarged portion 132 aof each magnet retaining hole.

According to the eighteenth embodiment, since the provision has beenmade of the enlarged portion 132 a in which the hole width of eachmagnet retaining hole adjacent the corresponding entwining portion 131is increased by the quantity V towards the entwining portion 131, eventhough the corresponding pincer portion 133 is deformed to protrudeinwardly of the associated magnet retaining hole 132 under the influenceof press stresses during formation of the corresponding entwiningportion by the use of a press work, the deformation can be accommodatedwithin the enlarged quantity V and, therefore, the permanent magnet caneasily be inserted without being disturbed. Also, since the enlargedportion 132 a has a length W that is small in correspondence with thelength of the adjacent entwining portion 131 and, also, the specificvalue of the quantity V is small and will decrease in response to inwarddeformation of the pincer portion 133, the gap with the permanent magnetis very minute and the coefficient of permeance of the magnetic circuitwill not decrease substantially, thereby securing a high-performancemotor characteristic.

It is to be noted that in the foregoing description the entwiningportion 131 has been described as positioned outside the associatedmagnet retaining hole 132, but it may be positioned inside theassociated magnet retaining hole and even in this case similar effectscan be obtained.

It is also to be noted that since if each of the permanent magnets ismade of a rare earth metal of, for example, Nd—Fe—B system, a highmagnetic force can be obtained and, therefore, the rotor and the motoras a whole can advantageously be manufactured in a compact size andlightweight.

It is further to be noted that although in the foregoing embodimentreference is made to the rotor of the synchronous motor employing thetwo poles, the present invention may not be limited thereto and may beequally applied to the rotor having, for example, four or more magneticpoles.

Again, although in any one of the foregoing embodiments the single polehas been formed by abutting two plate-like permanent magnets of the samepolarity in end-to-end fashion, the present invention may not be limitedthereto and the single pole may be formed by the use of a singlepermanent magnet or three or more plate-like permanent magnets of thesame polarity. Similarly, although the permanent magnets have beenemployed in the plate-like form, the present invention is not limitedthereto and the present invention is equally applicable to the rotoremploying permanent magnets of, for example, an arcuate shape or anyother suitable shape.

Nineteenth Embodiment (FIGS. 45 to 47)

A nineteenth preferred embodiment of the present invention will now bedescribed with reference to FIGS. 45 to 47, wherein FIG. 45 illustratesa longitudinal sectional view of the rotor used in the self-startingsynchronous motor of the type employing the permanent magnets accordingto the nineteenth embodiment, FIG. 46 is a transverse sectional view ofthe rotor and FIG. 47 is a plan view of an end plate. In these figures,reference numeral 141 represents a rotor, and reference numeral 142represents a rotor iron core made of a laminate of electromagnetic steelplates. Reference numeral 143 represents conductor bars which are moldedintegrally together with shortcircuit rings 144, positioned at axiallyopposite ends of the rotor iron core 142, by the use of the aluminum diecasting technique to form a starter squirrel cage conductor. Referencenumeral 145 represents permanent magnets, every two of which are held inend-to-end abutment to represent a generally V-shaped configuration andare so arranged that the two pairs of the permanent magnets 145 candefine two magnetic poles. Reference numeral 147 represents shortcircuitpreventive barriers for preventing shortcircuit of the magnetic fluxesbetween the permanent magnets of the different polarities and filled upwith aluminum die cast. Reference numeral 148 represents an end platemade of a non-magnetizable material and used of protection of thepermanent magnets 145, in which engagement holes 148 a are defined.Reference numeral 149 represents an axial hole defined in the rotor ironcore 142 so as to extend axially thereof, in which hole is filledaluminum 150 that is injected during the aluminum die casting to formthe starter squirrel cage conductor. The aluminum 150 filled in theaxial hole 149 has projections 150 a protruding outwardly from theaxially opposite ends of the rotor iron core 142. The end plates 148are, after the engagement holes 148 a have received therein theprojections 150 a, fixed to the respective axial end faces of the rotoriron core 142 by staking or crimping the projections 150 a to enlarge asshown by broken lines.

As hereinabove described, in the self-starting synchronous motoraccording to the nineteenth embodiment, since the projections 150 a usedto secure the end plates 148 to the axially opposite ends of the rotor141 are formed simultaneously with formation of the starter squirrelcage conductor by the use of the aluminum die casting technique andsince the end plates 148 can be firmly secured to the axially oppositeend faces of the rotor iron core 142 merely by staking or crimping theprojections 150 a, the cost for the material and the number ofassembling steps can be considerably reduced as compared with the priorart in which bolts are employed, thereby making it possible to providean inexpensive self-stating synchronous motor of the kind employing thepermanent magnets.

Twentieth Embodiment (FIGS. 48 to 50)

A twentieth preferred embodiment of the present invention will now bedescribed with reference to FIGS. 48 to 50, wherein FIG. 48 is alongitudinal sectional view of the self-starting permanent magnetsynchronous motor, FIG. 49 is a plan view of the end plate used in thesynchronous motor shown in FIG. 48, and FIG. 50 is a cross-sectionalview taken along the line C-C′ in FIG. 49. As shown in FIG. 48, theshortcircuit rings 144 a are formed so as to cover the end plates 152.Accordingly, the end plate 152 is integrated with the axially end faceof the rotor iron core 152 by means of the aluminum die casting used toform the starter squirrel cage conductor.

Referring to FIGS. 49 and 50, the end plate 152 is formed with twoprojections 152 a each having a respective hole 152 defined therein soas to extend completely across the thickness thereof. Prior to thealuminum die casting, the end plate 152 is secured to the correspondingend face of the rotor iron core 142 with the projections 152 aprotruding through the holes 149 to thereby position the respective endplate 152 so that the end plate 152 will not displace during thealuminum die casting in which a high pressure may act on the end plate152 to allow the end plate 152 to be firmly connected to the associatedend face of the rotor iron core 142 without being displaced in position.On the other hand, the end plate 148, the end plate 148 is, as is thecase with that in the previously described nineteenth embodiment, fixedto the end face of the rotor iron core 142 by staking or crimping theprojections 150 a after the end plate 148 has been engaged with theprojections 150 a for fixing the end plate.

As hereinabove described, since the end plate 152 is integrallyconnected with the rotor iron core 142 by means of the aluminum diecasting, a job of securing the end plate by staking or crimping theprojections 150 a has to be performed only in association with the endplate 148 and, therefore, as compared with the previously describednineteenth embodiment, the number of assembling steps can further bereduced.

Twenty-first Embodiment (FIGS. 51 and 52)

A twenty-first preferred embodiment of the present invention will bedescribed with reference to FIGS. 51 and 52, wherein FIG. 51 illustratesa longitudinal sectional view of the rotor used in the self-startingsynchronous motor and FIG. 52 is a plan view of an electromagnetic steelplate positioned at an axial end of the rotor iron core used in therotor of FIG. 51. Referring to FIGS. 51 and 52, the electromagneticsteel plate 160 positioned at the axial end of the rotor iron core 142having conductor bar slots 161, barrier holes 162 for preventing themagnetic flux shortcircuit, holes 149 and a bearing hole 150 all definedtherein is of the same shape as that used at a different position, butno magnet retaining hole 146 defined therein. Although thiselectromagnetic steel plate 160 is manufactured by blanking with the useof the same core dies as used for the other electromagnetic steelplates, since mold pieces used to form the magnet retaining holes 146 inthe electromagnetic steel plate 160 by the use of a blanking techniqueare of a type that can be removably mounted on a die assembly, it iseasy to avoid formation of the magnet retaining holes 146 in theelectromagnetic steel plate 160 at the time the latter is blanked offfrom a metal sheet. Accordingly, the rotor iron core 142 can beintegrally formed together with the electromagnetic steel plate 160 and,if this is aluminum die cast, the starter squirrel cage conductor can beformed.

Because of the structure described-above, the end plate on the other endis needed and, as is the case with the previously described twentiethembodiment, a job of securing the end plate by staking or crimping theprojections 150 a has to be performed only in association with the endplate 148 and, therefore, as compared with the previously describednineteenth embodiment, the number of assembling steps can further bereduced.

Twenty-second Embodiment (FIGS. 53 and 54)

A twenty-second preferred embodiment of the present invention will nowbe described with reference to FIGS. 53 and 54, wherein FIG. 53 is aplan view of the electromagnetic steel plate at the axial end of therotor iron core and FIG. 54 is a fragmentary enlarged view showing aportion of the rotor 141.

Referring to FIGS. 153 and 154, reference numeral 162 represents anelectromagnetic steel plate disposed at an axial end of the rotor ironcore 141, and reference numeral 164 represents a projection protrudinginwardly of the permanent magnets 154 at a location where theelectromagnetic steel plate 163 engages the permanent magnets 145.Accordingly, the permanent magnets 145 are axially positioned with theprojection 164 in the electromagnetic steel plate 163 brought intoengagement therewith.

According to the embodiment shown in FIGS. 53 and 54, shortcircuit ofthe magnetic fluxes between the front and rear, different poles of thepermanent magnets 145 through the electromagnetic steel plate 163 can bereduced considerably, thereby to increase the performance of the motor.It is to be noted that although this electromagnetic steel plate 163 ismanufactured by blanking with the use of the same core dies as used forthe other electromagnetic steel plates, since mold pieces used to formthe projection 163 are of a type that can be removably mounted on a dieassembly, the rotor iron core 142 can easily be formed integrallytogether with the electromagnetic steel plate 163.

Twenty-third Embodiment (FIGS. 55 to 57)

A twenty-third embodiment of the present invention will be describedwith reference to FIGS. 55 to 57, wherein FIG. 55 is a longitudinalsectional view of the complete rotor used in the self-startingsynchronous motor according to this embodiment, FIG. 56 is alongitudinal sectional view of the rotor before the end plates arefixed, and FIG. 57 is an end view of the rotor shown in FIG. 56.Referring to FIGS. 56 and 57, the end plate 171 has its outer peripheryformed with radial projections 171 a and, on the other hand, theshortcircuit ring 170 formed by the aluminum die casting has an innerperiphery formed with a radial recesses 170 a complemental in shape tothe radial projections 171 a in the end plate 171. After the radialprojections 171 a in the end plate 171 have been engaged in thecorresponding radial recesses 170 a in the shortcircuit ring 170,peripheral portions of the radial recesses 170 a in the shortcircuitring 170 are axially pressed to deform as shown by 170 b in FIG. 55 tothereby fix the end plate 171 to the rotor iron core 2.

According to the twenty-third embodiment, fixing of the end plate 171can easily be accomplished merely by pressing the radial recesses 170 ain the shortcircuit ring 170 to deform in the manner described aboveand, therefore, the number of assembling steps can advantageously bereduced.

It is to be noted that where the permanent magnets is made of a rareearth metal of, for example, Nd—Fe—B system, a strong magnetic force canbe obtained and, therefore, the rotor as well as the motor as a wholecan be manufactured in a compact size and lightweight.

It is also to be noted that in any one of the foregoing embodiments therotor has been shown having two magnetic poles, it may have four or moremagnetic poles. In addition, although in any one of the foregoingembodiments the single pole has been formed by abutting two plate-likepermanent magnets of the same polarity in end-to-end fashion, thepresent invention may not be limited thereto and the single pole may beformed by the use of a single permanent magnet or three or moreplate-like permanent magnets of the same polarity. Similarly, althoughthe permanent magnets have been employed in the plate-like form, thepresent invention is not limited thereto and the present invention isequally applicable to the rotor employing permanent magnets of, forexample, an arcuate shape or any other suitable shape.

Twenty-fourth Embodiment (FIGS. 60 to 62)

A twenty-fourth preferred embodiment of the present invention will nowbe described with reference to FIGS. 60 to 62, wherein FIG. 60illustrates a longitudinal sectional view of the rotor used in theself-starting synchronous motor according to this embodiment, FIG. 61 isa transverse sectional view of the rotor shown in FIG. 60 and FIG. 62 isa fragmentary enlarged view showing an encircled portion indicated by196 in FIG. 61.

Referring now to FIGS. 60 to 62, reference numeral 181 represents arotor, and reference numeral 182 represents a rotor iron core made of alaminate of electromagnetic steel plates. Reference numeral 183represents conductor bars that are formed integrally together withshortcircuit rings 184, positioned at axially opposite ends of the rotoriron core 182, by the use of an aluminum die casting technique to form astarter squirrel cage conductor. Reference numeral 185 representspermanent magnets accommodated within magnet retaining holes 186, witheach pair of plate-like permanent magnets 185 of the same polaritybutted end-to-end in a generally V-shaped configuration to form a singlerotor magnetic pole. Since four permanent magnets 185 are employed inthe rotor, two rotor magnetic poles are formed and, thus, the rotor as awhole has two magnetic poles.

A bridge portion indicated by 187 is so shaped as to have its widthincluding a narrow portion 187 a and a large-width portion 187 bincreasing in width in a direction radially outwardly from the narrowportion 187 a. Shortcircuit of the magnetic fluxes between front andrear, opposite poles of the permanent magnets 185 can advantageously beprevented since magnetic saturation takes place at the narrow portion187 a.

Also, since an air space 188 is defined between each of respective endfaces 185 a of the neighboring permanent magnets 185 and the bridgeportion 187, shortcircuit of the magnetic fluxes between the oppositepoles within the end faces 185 a of the neighboring permanent magnets185 can advantageously be avoided.

Reference numeral 189 represents barrier slots for prevention of themagnetic flux shortcircuit that are defined between the neighboringpermanent magnets 185 of the different polarities, which slots arefilled up with aluminum injected during the aluminum die casting. Abridge portion 191 of the rotor iron core 182 between each barrier-slot189 and each magnet retaining hole 186 is so shaped as to have a smallwidth, and at this bridge portion 191, magnetic saturation takes placeto prevent the magnetic fluxes emanating from the opposite poles of thepermanent magnets 185 from shortcircuiting. Also, an air space 192 isformed between an end face of each permanent magnet 185 and the adjacentbridge portion 191 to prevent the magnetic fluxes from the oppositepoles within the end faces of the permanent magnets 185 fromshortcircuiting. Reference numeral 193 represents an end plate made of anon-magnetizable material for protecting the permanent magnets 185. Thisend plate 193 is riveted to axially opposite end faces of the rotor ironcore 182 by means of rivet pins 194. Reference numeral 195 represents abearing hole defined in the rotor.

According to the twenty-fourth embodiment, the rotor 181 can beassembled by embedding the permanent magnets 185 in the respectivemagnet retaining holes 186 after the starter squirrel cage conductor hasbeen formed by the aluminum die casting in the rotor iron core 182 madeof a laminate of the electromagnetic steel plates, and subsequentlyriveting the end-plate 193 to each of the axially opposite end faces ofthe rotor iron core 182 by means of the rivet pins 194.

While after the aluminum die casting the shortcircuit rings will shrinkin a radial direction during cooling of the aluminum, the rotor ironcore 182 is also affected by a radially inwardly acting shrinkagestress. However, since the bridge portion 191 of the rotor iron core 182is provided on each sides of each of the barrier slots 189 at a locationadjacent the respective barrier slot 198 as shown in FIG. 58, a strengthagainst the shrinkage stress is so high that circumferential shrinkagestrains of an outer diameter of the rotor iron core 182 can be small.

On the other hand, since the bridge portion 187 is provided only at onelocation, strain acting in an inner diametric direction of the rotoriron core 182 at this portion is large. In order to avoid this, thelength in a radial direction of the narrow portion 187 a of the bridgeportion 187 for prevention of the magnetic flux shortcircuit by magneticsaturation is reduced and, on the other hand, the large-width portion187 b is provided next to the narrow portion 187 a, wherefore thestrength against the radial shrinkage stress of the bridge portion 187as a whole is made strong to prevent the strain from occurring in aninner diametric direction of the rotor iron core 182 at a locationadjacent the bridge portion 187.

As such, the rotor iron core 182 can have an outer diameter of a shapesubstantially similar to the right round shape and, therefore, if theouter diameter thereof is so chosen at the time of blanking theelectromagnetic steel plates of the rotor iron core 182 that gap betweenthe outer diameter thereof and an inner diameter of the rotor iron corecan be of a predetermined dimension, a step of grinding or milling theouter diameter of the rotor iron core after the aluminum die casting toprovide the gap of the predetermined dimension can be dispensed with.

Although in any one of the foregoing embodiments the single pole hasbeen formed by abutting two plate-like permanent magnets of the samepolarity in end-to-end fashion, the present invention may not be limitedthereto and the single pole may be formed by the use of a singlepermanent magnet or three or more plate-like permanent magnets of thesame polarity. Similarly, although the permanent magnets have beenemployed in the plate-like form, the present invention is not limitedthereto and the present invention is equally applicable to the rotoremploying permanent magnets of, for example, an arcuate shape or anyother suitable shape.

Thus, according to the twenty-fourth embodiment of the presentinvention, not only can any possible shortcircuit of the magnetic fluxesbetween the permanent magnet be prevented to secure a high performance,but also the grinding of the outer diameter of the rotor is eliminated,thereby making it possible to provide the high-performance, inexpensiveself-starting synchronous motor.

Twenty-fifth Embodiment (FIG. 63)

FIG. 63 illustrates a plan view of an electromagnetic steel plate usedto form the rotor in the self-starting synchronous motor according tothis embodiment. Referring now to this figure, reference numeral 51represents an electromagnetic steel plate, a plurality of which arelaminated together to form the rotor iron core. After the rotor ironcore has been so formed, the rotor iron core is subjected to thealuminum die casting to form the starter squirrel cage conductor in therotor iron core. Reference numeral 203 represents magnet retainingholes; reference numeral 204 represents a bridge portion F for each pairof the permanent magnets; reference numeral 205 represents barrier slotsfor prevention of shortcircuit of the magnetic fluxes; reference numeral206 represents a bridge portion; reference numeral 207 represents rivetholes through which rivets are passed to secure the end plate to eachaxial end face of the rotor core; and reference numeral 208 represents abearing hole. The permanent magnets to be inserted after the aluminumdie casting are shown by double-dotted lines and the rotor has two rotormagnetic poles formed therein.

The electromagnetic steel plate 201 has an outer diameter that is set toan outer diameter R1 sufficient to allow a gap between the rotor and theinner diameter of the stator iron core at one end of the rotor tosatisfy a predetermined dimension, which outer diameter R1 progressivelyincreases towards a center point of the rotor magnetic pole so that theouter diameter R2 of the center portion of the rotor magnetic poles canbe greater than the outer diameter R1. By blanking the electromagneticsteel plate of the above described shape and laminating a predeterminednumber of the electromagnetic steel plates to form the rotor iron coreand after the starter squirrel cage conductor has been formed by the useof the aluminum die casting, the permanent magnets are mounted in therotor iron core.

After the aluminum die casting, the shortcircuit rings (not shown)formed on the axially opposite end faces of the rotor iron core of thestarter squirrel cage conductor undergo a shrinkage in a radialdirection as they are cooled, accompanied by a radial shrinkage of theouter diameter of the rotor iron core under the influence of a shrinkageforce of the shortcircuit rings.

At this time, since the rotor magnetic pole ends of the electromagneticsteel plates 201 of the rotor iron core have the bridge portion 206defined at two locations, the strength is so high against the shrinkagestress in the inner diametric direction that the outer diameter R1 ofthe rotor iron core will not vary virtually. However, since at thecenter portion of the rotor magnetic poles the bridge portion 264 isdefined only at one location, the strength is so low that the outerdiameter R2 of the rotor iron core will shrink in a radial directionunder the influence of the shrinkage stress. At this time, if thedimension of the outer diameter R2 is chosen to be R1 after shrinkage,the outer diameter of the rotor iron core as a whole can be maintainedat a substantially round shape.

It is to be noted that although in FIG. 63 the circle of the outerdiameter R1 after the shrinkage is shown by the double-dotted line, thedifference in dimension between R1 and R2 are shown exaggerated tofacilitate a better understanding.

Although in the foregoing embodiments the single pole has been formed byabutting two plate-like permanent magnets of the same polarity inend-to-end fashion, the present invention may not be limited thereto andthe single pole may be formed by the use of a single permanent magnet orthree or more plate-like permanent magnets of the same polarity.

According to the twenty-fifth embodiment of the present invention, sincethe outer diameter of the rotor iron core after the aluminum die castingattains a shape substantially similar to the right round shape, andsince the gap between it and the inner diameter of the stator iron corecan be formed by pre-blanking with the use of dies, there is no need togrind or mill the outer diameter of the rotor iron core and, therefore,the number of assembling steps can be reduced. Also, since the aluminumdie casting is carried out while the permanent magnets and the endplates have not yet been fitted, the job can be easily performed with nodefect parts occurring and, in view of those cumulative effect, theproductivity can be increased.

Although the present invention has been described in connection with thepreferred embodiments thereof with reference to the accompanyingdrawings, it is to be noted that various changes and modifications areapparent to those skilled in the art. Such changes and modifications areto be understood as included within the scope of the present inventionas defined by the appended claims, unless they depart therefrom.

1. A synchronous motor comprising: a stator including a stator iron corehaving two-pole windings wound therearound, said stator iron core havingan inner cylindrical surface; a rotor including a rotor iron corerotatably accommodated facing the inner cylindrical surface of thestator iron core, said rotor including a plurality of conductor bars,positioned adjacent an outer periphery of the rotor iron core, andshortcircuit rings, positioned at axially opposite ends of the rotoriron core, said conductor bars and shortcircuit rings being moldedtogether by aluminum die casting to form a starter cage conductor, saidrotor having a plurality of magnet retaining slots defined therein on aninner side of the conductor bars; and permanent magnets embedded withinthe magnet retaining holes in the rotor and defining two magnetic polesof different polarities; said shortcircuit rings having an innerdiameter positioned outwardly from associated magnet retaining holes, aninner diameter of the shortcircuit rings at a location adjacent one endof the magnetic poles being larger than an inner diameter at a locationadjacent an intermediate point of the magnetic poles.
 2. The synchronousmotor as recited in claim 1, wherein the inner diameter of theshortcircuit rings on a side adjacent the permanent magnets lies outsidethe magnet retaining holes in the rotor iron core; wherein an innerdiameter of one of the shortcircuit rings adjacent one of the magneticwherein an inner diameter of one of the shortcircuit rings adjacent oneof the magnetic poles is larger than an inner diameter adjacent a pointintermediate the magnetic poles; and wherein an inner diameter of atleast one other of the shortcircuit rings lies inwardly of at least partof the magnet retaining holes; said synchronous motor further comprisingan end plate comprising a non-magnetizable material positioned betweenthe at least one other shortcircuit ring and the rotor iron core,covering the magnet retaining holes.
 3. The synchronous motor as recitedin claim 1, wherein the inner diameter of the shortcircuit rings on oneside of the permanent magnets lies outside the magnet retaining holes inthe rotor iron core; wherein an inner diametric dimension of one of theshortcircuit rings adjacent one end of the magnetic poles is greaterthan an inner diametric dimension of the one of the shortcircuit ringsadjacent the intermediate point of the magnetic poles; and wherein theinner diametric dimension of the at least one other of the shortcircuitrings lies inwardly of at least a part of the magnet retaining holes;said rotor iron core comprising a plurality of electromagnetic steelplates, one of the electromagnetic steel plates being adjacent the atleast one other shortcircuit ring, not formed with the magnet retainingholes.
 4. The synchronous motor as recited in claim 1, wherein the innerdiameter of the shortcircuit rings on one side of the permanent magnetscomprises a shape lying along the magnet retaining holes in the rotoriron core.